libgit2 v0.26.7

This is a security release fixing the following list of issues:

• Submodule URLs and paths with a leading "-" are now ignored.
  This is due to the recently discovered CVE-2018-17456, which
  can lead to arbitrary code execution in upstream git. While
  libgit2 itself is not vulnerable, it can be used to inject
  options in an implementation which performs a recursive clone
  by executing an external command.

• When running repack while doing repo writes,
  packfile_load__cb() could see some temporary files in the
  directory that were bigger than the usual, and makes memcmp
  overflow on the p->pack_name string. This issue was reported
  and fixed by bisho.

• The configuration file parser used unbounded recursion to parse
  multiline variables, which could lead to a stack overflow. The
  issue was reported by the oss-fuzz project, issue 10048 and
  fixed by Nelson Elhage.

• The fix to the unbounded recursion introduced a memory leak in
  the config parser. While this leak was never in a public
  release, the oss-fuzz project reported this as issue 10127. The
  fix was implemented by Nelson Elhage and Patrick Steinhardt.

• When parsing "ok" packets received via the smart protocol, our
  parsing code did not correctly verify the bounds of the
  packets, which could result in a heap-buffer overflow. The
  issue was reported by the oss-fuzz project, issue 9749 and
  fixed by Patrick Steinhardt.

• The parsing code for the smart protocol has been tightened in
  general, fixing heap-buffer overflows when parsing the packet
  type as well as for "ACK" and "unpack" packets. The issue was
  discovered and fixed by Patrick Steinhardt.

• Fixed potential integer overflows on platforms with 16 bit
  integers when parsing packets for the smart protocol. The issue
  was discovered and fixed by Patrick Steinhardt.

• Fixed potential NULL pointer dereference when parsing
  configuration files which have "include.path" statements
  without a value.