debian/control: Make the mongodb metapackage arch-dependent.

Otherwise, the package would be available for architectures where its
dependencies would not be fulfilled.

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
debian/control: Set priority of packages to extra.

Unfortunately, libsnappy1 is priority extra on the archive, and mongodb
depends on it, which means that we have to be priority extra too.

This problem was detected by seeing:

    http://qa.debian.org/debcheck.php?dist=unstable&package=mongodb

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
debian/control: Mark libgoogle-perftools-dev as linux-amd64 linux-i386.

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>
debian/patches: Take some patches for ARM from Ubuntu.

Some of these patches came from RedHat.

The patch 0007-ARM-support... required manual patching, as the upstream code
changed slightly.

The patches were also rebuilt from a patch queue branch.

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>