proposal: add --disable-tests to www/firefox3 port

[Eitan Adler]

ac_add_options --disable-tests
    By default, many auxiliary test applications are built, which can
help debug and patch the mozilla source. Disabling these tests can speed
build time and reduce disk space considerably [1]

Most users don't need these tests built unless they plan on helping
debug and patch the mozilla source.

I think we should add it to MOZ_OPTIONS in www/firefox3.  If it exists
for firefox2 I propose adding it to firefox2 as well (especially since
firefox2 is going to be EOL soon).

[1] https://developer.mozilla.org/en/Configuring_Build_Options
-- 
Eitan Adler
GNU Key fingerprint: 2E13 BC16 5F54 0FBD 62ED 42B6 B65F 24AB E9C2 CCD1