tests: omit -p for external diff via extdiff extension for portability Before this patch, some tests using external "diff" command via extdiff extension fail on Solaris, because "-p" (show which C function each change is in) option isn't supported by system standard "diff" on Solaris, even though extdiff passes it to external "diff" by default. Fortunately, this non-portable option isn't important for (current, at least) tests using external "diff" command via extdiff extension. This patch omits "-p" for external "diff" command via extdiff extension for portability of tests, and adds check-code.py a rule to detect invocation of "diff" with "-p". Newly added check-code.py rule examines only lines generated by external "diff" with "-r", because strict examination might misidentify "hg diff -p" or other complicated lines consisting of "diff" string as wrong one. This patch is a part of making tests using external "diff" portable, and tests below aren't yet portable even after this patch. test-graft.t test-largefiles-update.t test-subrepo-deep-nested-change.t