When a RPM test build in a non-release branch is done,
the $MYSQL_BINDIR variable ends in "/usr"
(rather than in "/usr/lib" as in a RPM release build),
this made test "file_contents" fail.

A branch for this case is added to the test.
The test result is unchanged.



mysql-test/t/file_contents.test:
  Fight a problem in internal test builds:
  
  When a RPM test build in a non-release branch is done,
  the $MYSQL_BINDIR variable ends in "/usr"
  (rather than in "/usr/lib" as in a RPM release build),
  this made test "file_contents" fail.
  
  Because of this, the old logic did not recognize
  that a RPM build is done (trailing '/' missing!)
  and took the tar.gz branch.
  Just removing the trailing '/' from the "/usr" is
  not enough, as the logic for RPMs used to replace
  "/lib" which is not present at all; rather, a new
  branch was added.
  
  To help in case of future problems, the error messages
  for a failing "open()" now also report "$MYSQL_BINDIR".