Add support for imported files in perforce.
Review Request #7049 — Created March 12, 2015 and submitted
Perforce can integrate from a remote depot, which adds files using the 'import'
method. This change adds support for import, treating it like an add.
Ran unit tests.
Tool: Pyflakes Processed Files: rbtools/clients/perforce.py Tool: PEP8 Style Checker Processed Files: rbtools/clients/perforce.py