Expose begin/end information from StringMatch
Move plain-string comparison out of StringMatch[Full]

This makes semantics of those functions cleaner.
StripPatterns: use StringMatch, not BlockTextMatch

BlockTextMatch sets $(match) context, which is not needed in this
case.
Don't use BlockTextMatch in RlistFromSplitRegex

BlockTextMatch populates $(match) scope, which should not be
touched in RlistFromSplitRegex (closes Redmine #1875).
Merge pull request #1096 from dottedmag/bugfix/slow-readstringlist

Fix slow readstringlist() on large files