[CLEANUP] Add package-version.txt files
[CLEANUP] Mercurial-related data
[REORG] Final fix of file locations
[CLEANUP] Unused files
[CLEANUP] Add gitignores
[FIXUP] new sage-build script
[FIXUP] correct pipestatus location
[FIXUP] change default SAGE_BUILD_DIR
[FIXUP] make sage-env and basic startup not depend on the spkg directory
[FIXUP] sage-spkg: support local scripts
[FIXUP] copy csage, including headers
[FIXUP] sagenb: install into site-packages
[FIXUP] remove mecurial
[FIXUP] correct doctests for the git layout
[FIXUP] remove SAGE_DATA
[FIXUP] correct values in sage/env.py
[FIXUP] make it possible to download upstream tarballs
[FIXUP] remove symlinks for sage library

this is no longer needed since we don't clone
the library into different directories anymore
[FIXUP] new upgrade system
[FIXUP] Makefile: correct clean targets and fix a few other small things