osproc: increase stack size from 8k to 64k
osproc: use fork by default on Linux, clone if requested by useClone flag
Merge pull request #953 from zielmicha/vfork

osproc: increase stack size from 8k to 64k and disable useClone default
osproc: MacOSX workaround for lack of execvpe
osproc: MacOSX fix - if -> when
Merge pull request #957 from zielmicha/macosx-fix

osproc: MacOSX workaround for lack of execvpe