travis: don't install libgit2 for 'next' branch

We have our own libgit2 in a submodule, so this is unnecessary. While in
the area, update which version of libgit2 would be downloaded and remove
unnecessary CMake flags.

.travis.yml

@@ -2,14 +2,7 @@ language: go
 
 sudo: false
 
-install:
-  - cd "${HOME}"
-  - wget -O libgit2-0.22.1.tar.gz https://github.com/libgit2/libgit2/archive/v0.22.1.tar.gz
-  - tar -xzvf libgit2-0.22.1.tar.gz
-  - cd libgit2-0.22.1 && mkdir build && cd build
-  - cmake -DTHREADSAFE=ON -DBUILD_CLAR=OFF -DCMAKE_C_FLAGS=-fPIC -DCMAKE_BUILD_TYPE="RelWithDebInfo" -DCMAKE_INSTALL_PREFIX=/usr/local .. && make && sudo make install
-  - sudo ldconfig
-  - cd "${TRAVIS_BUILD_DIR}"
+install: ./script/install-libgit2.sh
 
 go:
   - 1.1

script/install-libgit2.sh

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+#
+# Install libgit2 to git2go in dynamic mode on Travis
+#
+
+set -ex
+
+# We don't want to build libgit2 on the next branch, as we carry a
+# submodule with the exact version we support
+if [ "x$TRAVIS_BRANCH" = "xnext" ]; then
+    exit 0
+fi
+
+cd "${HOME}"
+wget -O libgit2-0.22.3.tar.gz https://github.com/libgit2/libgit2/archive/v0.22.1.tar.gz
+tar -xzvf libgit2-0.22.3.tar.gz
+cd libgit2-0.22.1 && mkdir build && cd build
+cmake -DTHREADSAFE=ON -DBUILD_CLAR=OFF -DCMAKE_BUILD_TYPE="RelWithDebInfo" .. && make && sudo make install
+sudo ldconfig
+cd "${TRAVIS_BUILD_DIR}"