run-tests: make per-line condition support testcase names 7340465bd added multiple test cases support. The latter has a problem - output lines cannot be made conditional with `#if`: ``` # COUNTEREXAMPLE: DOES NOT WORK #testcases A B $ command-foo common ouput #if A A's ouput #else B's ouput #endif common ouput ``` That's not trivial to fix (even if it works in test, `run-tests.py -i` may be suboptimal because diff algorithm does not know how to skip the `#if` lines, even if it does, it may have trouble figuring out whether a changed line belongs to inside a `#if` block or outside). Matching output lines conditionally is useful. 4eec2f04a added per-line condition support for hghave. This patch extends that to also support test case names. Differential Revision: https://phab.mercurial-scm.org/D466