Msys(2) Improvements

[cr1901]

I've have the date portion of this PR fixed locally since checks oh, November 2016, but I never got around to actually submitting a PR :). Better late than never?

This PR improves using rsync_tmbackup.sh in the msys2 environment (alternative to cygwin which creates binaries which don't depend on the cygwin dll). Date parsing to detect old backups to-be-purged and detecting an already-running backup for the directory is now functional.

Detecting existing processes requires procps, as it does on cygwin (pacman -S procps). Running procps has a few minor warnings that are unavoidable for now:

$ ./msys.sh
2.4+ kernel w/o ELF notes? -- report this
Warning: bad ps syntax, perhaps a bogus '-'? See http://procps.sf.net/faq.html

As I can't test cygwin at this moment, I don't want to modify the commands shared between msys and cygwin to detect existing backups for now- just in case there's subtle command-line breakage (It shouldn't cause any problems to remove a "-", but you never know!).