Normalize whitespace in osproc.nim.
Introduce poEvalCommand, poUsePath, fix remaining quoting issues.

- poUsePath is now an alias for poUseShell.
- poEvalCommand should be used when shell evaluation is really needed.
It passes `command` directly to shell/winapi. Requires `args` parameter
to be empty.
Merge branch 'osproc' into devel

Conflicts:
	lib/posix/posix.nim
	lib/pure/osproc.nim
Merge branch 'devel' of https://github.com/Araq/Nimrod into devel

Conflicts:
	lib/pure/osproc.nim
Merge pull request #830 from zielmicha/osproc

osproc: introduce poEvalCommand, poUsePath, fix remaining quoting issues.