scons: import package macros from old SConstruct
scons: fix typo and remove old SConstruct backup
scons: define PM_VERSION
scons: import then export environment for this SConscript
scons: include lib/libpacman always. extend SConscript to compile libpacman.
most everything here includes pacman.h, so no real choice here.
scons: import curl include path and pkg-config info for libarchive / libcurl