rose_arch: check update with mtime and size

As an alternate solution to MD5 checksum, which may be slow for large
files.
rose_arch: test update with mtime and size change

As well as content change.
Clarify "timeout".
Merge pull request #954 from arjclark/rose-doc-explain-timeout

Clarify "timeout".
Merge branch 'master' into rose_arch.check.mtime-and-size
Merge remote branch 'origin/rose_arch.check.mtime-and-size' into rose_arch.check.mtime-and-size
rose_arch: mtime and size: cache relative name
Merge pull request #949 from matthewrmshin/rose_arch.check.mtime-and-size

rose_arch: modified time and size update check