Make file grouping less aggressive.
The file-grouping logic was grouping files named as foo1bar.ext
,
foo2bar.ext
, which was an overkill. That ended up matching dissimilar
files like foo.2dm
and foo.3dm
. Cleanup that up.
Also added a test TestFileSequenceParser
that tests for file grouping
patterns.
Fixes #17313 (closed).