backport of .gitignore files from master

Signed-off-by: Loic Dachary <loic@dachary.org>
Merged in dachary/jerasure/wip-gitignore-v2 (pull request #13)

backport of .gitignore files from master
make galois_init_default_field(int w) extern

So that the application can initialize gfp_array and gfp_is_composite
instead of relying on initialization happening implicitly when the
multiply or xor functions are called. The init function can be called
once when the application guarantees thread safety. And the multiply and
xor functions can be called from multiple threads without risking races.

Signed-off-by: Loic Dachary <loic@dachary.org>
(cherry picked from commit 5c9577172c9ba29890c821692dd4a9f9790b20d8)
Merged in dachary/jerasure/wip-init-v2 (pull request #18)

make galois_init_default_field(int w) extern
silence warning about bestrow used uninitialized

Signed-off-by: Loic Dachary <loic@dachary.org>
(cherry picked from commit cdc99aadc986c165e66574c633e7202eb830b8f9)
Merged in dachary/jerasure/wip-compilation-warning-v2 (pull request #19)

silence warning about bestrow used uninitialized