[entropy.spm] PortagePlugin: pass fd_pipes to doebuild()

This will redirect portage.doebuild() output to our log file
Release Entropy 212
Tagging Entropy version 212
[entropy.server] nit: drop useless empty line
[entropy.spm] SpmPlugin: add installed_mtime() public method, bump API
[entropy.server] extended_dependencies_test: use SpmPlugin.installed_mtime()

Cache validation must use SpmPlugin.installed_mtime() as part of the
cache key when Spm() installed packages repository is used.
Release Entropy 213
Tagging Entropy version 213
[entropy.spm] PortagePlugin.installed_mtime: consider parent dir mtime
Merge remote-tracking branch 'upstream/master'