ebuild: multi-pkg for remove/purge, optimizations
ebuild: multi-pkg for remove/purge, optimizations

This commit brings support for the "pkgs" argument to the remove and
purge functions. In addition, the use of __context__ has been added to
list_pkgs. All functions which modify the package database now clear the
__context__ variable before running list_pkgs again to ensure that
changes are detected.

saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt,saltstack/salt