[package] Use target-specific variables to propagate filenames.

We now use target-specific variables to propagate the last built
package's filename to package.mk (whose responsibility it now is to
record such). Cleaned up a couple targets.

From: Dustin L. Howett <dustin@howett.net>

git-svn-id: http://svn.howett.net/svn/theos/trunk@623 4410221e-0ddf-4ce3-99c0-2db6c0dbc727
[makefiles] Include stage and package from common instead of master/rules.

From: Dustin L. Howett <dustin@howett.net>

git-svn-id: http://svn.howett.net/svn/theos/trunk@624 4410221e-0ddf-4ce3-99c0-2db6c0dbc727
[rules] Use __simplify instead of a manual simulacrum of it for object file tagging.

From: Dustin L. Howett <dustin@howett.net>

git-svn-id: http://svn.howett.net/svn/theos/trunk@625 4410221e-0ddf-4ce3-99c0-2db6c0dbc727
[makefiles] Make some variables simply-expanded where they don't need to be recursively-expanded.

From: Dustin L. Howett <dustin@howett.net>

git-svn-id: http://svn.howett.net/svn/theos/trunk@626 4410221e-0ddf-4ce3-99c0-2db6c0dbc727
[makefiles] Suppress some "Nothing to be done for ..." warnings by giving some targets blank command sets.

From: Dustin L. Howett <dustin@howett.net>

git-svn-id: http://svn.howett.net/svn/theos/trunk@627 4410221e-0ddf-4ce3-99c0-2db6c0dbc727
[package] Package versioning overhaul and custom package versions.

- Decouple package_version from control file parsing (kill most of its
  complexity without trashing the existing version number data.)
- Move build number bumping into an includable variable
  (VERSION.INC_BUILD_NUMBER)
- Add support for a schema'd PACKAGE_VERSION variable so that the user
  may override version number generation.
- Offer an alternative to THEOS_PACKAGE_VERSION in the deprecation
  warning.
- Include the default version number format as
  _THEOS_PACKAGE_DEFAULT_VERSION_FORMAT.
- Offer variables the user can place in his PACKAGE_VERSION to have
  theos generate parts of them (build number, extraversion.)
  (VERSION.INC_BUILD_NUMBER and VERSION.EXTRAVERSION.)

From: Dustin L. Howett <dustin@howett.net>

git-svn-id: http://svn.howett.net/svn/theos/trunk@628 4410221e-0ddf-4ce3-99c0-2db6c0dbc727