Default timeout setting helper in process module does not work as intended

[lukpueh]

Description of issue or feature request:
#202 added a helper function with the intention of deferring the evaluation of the default argument SUBPROCESS_TIMEOUT, used in two functions of the process module, until invocation of these functions.
This should have made it possible to modify SUBPROCESS_TIMEOUT via the settings module, where it is defined originally, even after importing the process module.

Unfortunately, this does not work as intended, because the helper function and thus the default SUBPROCESS_TIMEOUT is still evaluated only once at import time.

Note: This issue is a side-effect of the non-intuitive usage pattern of expecting user interaction via patching globals in the settings module, which is documented in #219. IMHO it is okay to fix this issue together with #219.

Current behavior:
Default argument is evaluated at function import time.

Expected behavior:
Default argument is evaluated at function invocation time.