Imported the ARM-7 port as of hg changeset 129 / Aug 08 2012
Add ignored build products to .gitignore
Fix two bugs: one in cant.add, and another in the machine-address primop.

The machine-address primop is used, in particular, to get hash codes
for eq-hash-tables; but the code there assumes that the results will
be non-negative, so it is not enough to just blindly shift left by 2
places.  Instead I copied the implementation from the Sparc target
(sparcprim-part1.sch), which zeros out the bottom four bits and then
shifts *right* by two.

We might want to revise this primop's name to reflect the fact that it
is not actually producing the machine-address, at least not in a
information-lossless fashion.
Our cleaning utility has needed an update since the long-ago directory
rearrangement.
Added new linux-arm-el value for host:os.
Make debugging hashtable.sch easier by reporting the key along with
the hashcode when reporting the assertion violation.
Added include of stdint.h to get the various int_t typedefs.

I'm pretty sure I needed this to get things building on ARM Chromebook
Ubuntu.
Updated stress-test benchmark driver script to match new larceny.bin interface.
Merge pull request #684 from pnkfelix/lth-arm-port

Lth arm port