gnu: libgit2: Update to 0.26.4 [fixes CVE-2018-11235].

* gnu/packages/version-control.scm (libgit2): Update to 0.26.4.
(source): Adjust patch name.
* gnu/packages/patches/libgit2-0.25.1-mtime-0.patch: Rename to ...
* gnu/packages/patches/libgit2-mtime-0.patch: ... this.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.

gnu/local.mk

@@ -861,7 +861,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/libevent-2.1-skip-failing-test.patch	\
   %D%/packages/patches/libexif-CVE-2016-6328.patch		\
   %D%/packages/patches/libexif-CVE-2017-7544.patch		\
-  %D%/packages/patches/libgit2-0.25.1-mtime-0.patch		\
+  %D%/packages/patches/libgit2-mtime-0.patch			\
   %D%/packages/patches/libgdata-fix-tests.patch			\
   %D%/packages/patches/libgdata-glib-duplicate-tests.patch	\
   %D%/packages/patches/libgnome-encoding.patch			\

gnu/packages/version-control.scm

@@ -419,7 +419,7 @@ everything from small to very large projects with speed and efficiency.")
 (define-public libgit2
   (package
     (name "libgit2")
-    (version "0.26.0")
+    (version "0.26.4")
     (source (origin
               (method url-fetch)
               (uri (string-append "https://github.com/libgit2/libgit2/"
@@ -427,8 +427,8 @@ everything from small to very large projects with speed and efficiency.")
               (file-name (string-append name "-" version ".tar.gz"))
               (sha256
                (base32
-                "1b3figbhp5l83vd37vq6j2narrq4yl9pfw6mw0px0dzb1hz3jqka"))
-              (patches (search-patches "libgit2-0.25.1-mtime-0.patch"))
+                "15ybzypyggx64ba7i0zxnnbvzh7z34fcrkwk2xj54kmv1dha4br9"))
+              (patches (search-patches "libgit2-mtime-0.patch"))
 
               ;; Remove bundled software.
               (snippet '(begin