Added a filter to remove buildenv's warnings.

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.
diff --git a/ide/emacs/android-common.el b/ide/emacs/android-common.el
index 7bf82a2..cebd087 100644
--- a/ide/emacs/android-common.el
+++ b/ide/emacs/android-common.el
@@ -43,6 +43,14 @@
   :group 'android)
 
 ;;;###autoload
+(defcustom android-compilation-no-buildenv-warning t
+  "If not nil, suppress warnings from the build env (Makefile,
+bash) from the compilation output since they interfere with
+`next-error'."
+  :type 'boolean
+  :group 'android)
+
+;;;###autoload
 (defcustom android-product-alias-map nil
   "Alist between product targets (declared in buildspec.mk) and actual
  product build directory used by `android-product'.