Merge branch 'pw/p4-symlinked-root'

"git p4" did not behave well when the path to the root of the P4
client was not its real path.

* pw/p4-symlinked-root:
  git p4: avoid expanding client paths in chdir
  git p4 test: should honor symlink in p4 client root
  git p4 test: make sure P4CONFIG relative path works