record: check patch name is valid before prompting in qrecord

mq: use checkpatchname This also fixes a bug where qrename would allow renaming a patch to a reserved name.

mq: wrap patch file name checks in a function

pure parsers: properly detect corrupt index files This new Python code should be equivalent in behavior to the if statement at line 312 of parsers.c. Without this, the pure-python parsers improperly ignore truncated revlogs as created in test-verify.t.