Also hint that the "all" target can be used

Author: philderbeast

cabal-install/src/Distribution/Client/CmdRepl.hs

@@ -583,7 +583,7 @@ reportProjectNoTarget projectFile pkgs =
       Flag "" -> Nothing
       Flag n -> Just $ quotes (text n)
       _ -> Nothing
-    pickComponent = text "pick a single [package:][ctype:]component as target for the REPL command."
+    pickComponent = text "pick a single [package:][ctype:]component (or all) as target for the REPL command."
 
 validatedTargets
   :: Verbosity

cabal-testsuite/PackageTests/ReplProjectTargetTwoPkgs/cabal.out

@@ -8,26 +8,26 @@ Configuring library for fake-package-0...
 # checking repl command with a 'cabal.project' and no project options
 # cabal repl
 Error: [Cabal-7076]
-Please pick a single [package:][ctype:]component as target for the REPL command. The packages from which to select a component in 'cabal.project', the implicit default as if `--project-file=cabal.project` was added as a command option, are:
+Please pick a single [package:][ctype:]component (or all) as target for the REPL command. The packages from which to select a component in 'cabal.project', the implicit default as if `--project-file=cabal.project` was added as a command option, are:
  - pkg-one
  - pkg-two
 # checking repl command using an explicit 'some.project'
 # cabal repl
 Error: [Cabal-7076]
-Please pick a single [package:][ctype:]component as target for the REPL command. The packages in 'some.project' from which to select a component target are:
+Please pick a single [package:][ctype:]component (or all) as target for the REPL command. The packages in 'some.project' from which to select a component target are:
  - pkg-one
  - pkg-two
 # checking repl command using an explicit 'reverse.project', listing packages in reverse order
 # cabal repl
 Error: [Cabal-7076]
-Please pick a single [package:][ctype:]component as target for the REPL command. The packages in 'reverse.project' from which to select a component target are:
+Please pick a single [package:][ctype:]component (or all) as target for the REPL command. The packages in 'reverse.project' from which to select a component target are:
  - pkg-one
  - pkg-two
 # checking repl command with an 'empty.project' with no packages
 # cabal repl
 Warning: There are no packages or optional-packages in the project
 Error: [Cabal-7076]
-There are no packages in 'empty.project'. Please add a package to the project and pick a single [package:][ctype:]component as target for the REPL command.
+There are no packages in 'empty.project'. Please add a package to the project and pick a single [package:][ctype:]component (or all) as target for the REPL command.
 # checking repl command with a missing 'missing.project'
 # cabal repl
 # checking repl command with a missing 'missing.project'

cabal-testsuite/PackageTests/ReplProjectTargetTwoPkgs/default-repl.txt

@@ -1,3 +1,3 @@
-Please pick a single [package:][ctype:]component as target for the REPL command. The packages from which to select a component in 'cabal.project', the implicit default as if `--project-file=cabal.project` was added as a command option, are:
+Please pick a single [package:][ctype:]component (or all) as target for the REPL command. The packages from which to select a component in 'cabal.project', the implicit default as if `--project-file=cabal.project` was added as a command option, are:
  - pkg-one
  - pkg-two

cabal-testsuite/PackageTests/ReplProjectTargetTwoPkgs/reverse-repl.txt

@@ -1,3 +1,3 @@
-Please pick a single [package:][ctype:]component as target for the REPL command. The packages in 'reverse.project' from which to select a component target are:
+Please pick a single [package:][ctype:]component (or all) as target for the REPL command. The packages in 'reverse.project' from which to select a component target are:
  - pkg-one
  - pkg-two

cabal-testsuite/PackageTests/ReplProjectTargetTwoPkgs/some-repl.txt

@@ -1,4 +1,4 @@
-Please pick a single [package:][ctype:]component as target for the REPL command. The packages in 'some.project' from which to select a component target are:
+Please pick a single [package:][ctype:]component (or all) as target for the REPL command. The packages in 'some.project' from which to select a component target are:
  - pkg-one
  - pkg-two