tests: rewrite umovestr2.test without using grep

The regular expression generated by umovestr2.c on systems with large
page size is too big for GNU grep.  Rewrite the test to use diff
instead of grep.

* tests/umovestr2.test: Use match_diff instead of match_grep.
* tests/umovestr2.c (main): Convert output from regexp to plain text.
2 files changed