tests: use pdiff instead of diff for portability "diff" command might cause redundant message, "No differences encountered" on Solaris for example. But suppressing option like "-q" isn't portable, because POSIX specification doesn't define it. pdiff script was introduced by b59ef0c21405 to stabilize output of standard diff command on each platforms.

tests: make pdiff return appropriate exit code at comparison of files Before this patch, pdiff script returns 0, even if diff is detected. This issue doesn't cause failure of tests using it, if it is invoked via extdiff extension, because extdiff itself examines changes between specified revisions and decides exit code. BTW, this patch ignores recursive comparison case, because: - there is no portable way for current while-read based implementation to return 1 at detecting changes - it isn't yet needed to replace direct "diff -r" invocation by pdiff for portability