merge: fix UnboundLocalError (issue3791) A wrong variable name was introduced in 384df4db6520 for a case without test coverage. The variable name is fixed and a test case is introduced.

parsers: fix memleak of revlog cache entries on strip Since 12a852c7c763, raw_length can be reduced on strip, but corresponding cache entries still have refcount. They are not dereferenced by _index_clearcache(), and never freed. To reproduce the problem, run "hg pull" and "hg strip null" several times in the same process.