Warnings about makefiles and build scripts interfere
with `next-error'. If you are interested only in the
errors from the source file, a custom variable allows
you to nuke build env warnings.
The filter is registered as a compilation-filter-hook.
All the commands output go to an *Android Output* buffer which
gets cleaned up before each command run.
Fixed a compilation bug, building from the top Makefile was not
generating a new image.
Moved common functions in a new android-common.el file.
Declared a customizable variable to control the number
of jobs used during the make process.
In android-compile, call compile interactively to honor
the compile-read-command feature to give the user the opportunity
to edit the command (e.g add the snod target)
