Fix globs matching files with wildcard characters in the name

Globs that match a file that looks like a glob were causing duplicate
results because the prefix match would then re-match the
filename as a wildcard.  Add escaping to prevent re-matching.

Also add tests for globs on files with wildcards, tests for
? and [a-z] glob matches supported by filepath.Match, and tests
for escaped wildcard characters.

Test: glob_test.go
Change-Id: Id11a754863979bb36cca0dbd18ea2e76dd1470e3