patch: security bump to version 2.7.6

Fixes CVE-2016-10713: Out-of-bounds access within pch_write_line() in
pch.c can possibly lead to DoS via a crafted input file.

Add upstream patch fixing CVE-2018-6951: There is a segmentation fault,
associated with a NULL pointer dereference, leading to a denial of
service in the intuit_diff_type function in pch.c, aka a "mangled
rename" issue.

This bump does NOT fix CVE-2018-6952. See upstream bug #53133
(https://savannah.gnu.org/bugs/index.php?53133

).

Add license file hash.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>