.gitignore update

headers_install by default puts headers into usr/include/ .
They're auto-generated, so should be ignored.

Same for *.orig, *.rej .

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>