Unified int primitives fix

This reverts the revert of #294 and fixes the FFI bug in the executor.  test025 still fails with a segfault, but according to Edwin on IRC, he has a fix for that laying around.

````
$ make test
make -C test
make[1]: Entering directory `/home/drc/Documents/Code/Idris/Idris-dev/test'
perl ./runtest.pl all
Running reg001...success
Running reg002...success
Running reg003...success
Running reg004...success
Running reg005...success
Running reg006...success
Running reg007...success
Running reg008...success
Running reg009...success
Running reg010...success
Running reg011...success
Running reg012...success
Running reg013...success
Running reg014...success
Running reg015...success
Running reg016...success
Running reg017...success
Running test001...success
Running test002...success
Running test003...success
Running test004...success
Running test005...success
Running test006...success
Running test007...success
Running test008...success
Running test009...success
Running test010...success
Running test011...success
Running test012...success
Running test013...success
Running test014...success
Running test015...success
Running test016...success
Running test017...success
Running test018...success
Running test019...success
Running test020...success
Running test021...success
Running test022...success
Running test023...success
Running test024...success
Running test025.../tmp/idris32326: In function ‘_idris_Effect_46_Memory_46_do_95_memset’:
/tmp/idris32326:2431:5: warning: passing argument 3 of ‘idris_memset’ makes pointer from integer without a cast [enabled by default]
In file included from /tmp/idris32326:2:0:
/home/drc/.cabal/share/idris-0.9.8/rts/idris_rts.h:211:6: note: expected ‘VAL’ but argument is of type ‘uint8_t’
/tmp/idris32326: In function ‘_idris_Effect_46_Memory_46_do_95_poke’:
/tmp/idris32326:2557:9: warning: passing argument 3 of ‘idris_poke’ makes pointer from integer without a cast [enabled by default]
In file included from /tmp/idris32326:2:0:
/home/drc/.cabal/share/idris-0.9.8/rts/idris_rts.h:213:6: note: expected ‘VAL’ but argument is of type ‘uint8_t’
Segmentation fault
FAILURE
Running test026...success
make[1]: *** [test] Error 1
make[1]: Leaving directory `/home/drc/Documents/Code/Idris/Idris-dev/test'
make: *** [test] Error 2

````