Add support to scan specific files only

Review Request #9530 — Created Jan. 25, 2018 and submitted — Latest diff uploaded




PMD supports multiple languages. But most checks
are for java files only as the other languages
are for CPD only or requires manually added checks.

This features allows to increase the performance
of review checks as it is not necessary to run PMD
for all files in a diff if only .java has enabled
checks. Also this avoid but not fix bug #4633.

Also increase timeout as big patches with a lot
of files will take some time to be finished.

Fixes conflicting variable name 'f' introduced by
changeset f95629e2739037bd0e0f289875f710f2da4aa2dd
by mistake.

Added some binary files with another file extension
and saw that it wasn't scanned.

Enabled java extension only and added a java file.
Saw that the check found correct issues.

Leave the extension setting empty and saw that it
still found correct issues in uploaded java patch.

Used "cpp" as file extension and saw that it
ignores java files.