travis: Use a fix revision for Botan and speed up subsequent builds via ccache

.travis.yml

@@ -7,6 +7,8 @@ compiler:
   - gcc
   - clang
 
+cache: ccache
+
 before_install:
   - travis_retry ./scripts/test.sh deps
   - travis_retry ./scripts/test.sh pydeps

scripts/test.sh

@@ -3,6 +3,8 @@
 
 build_botan()
 {
+	# same revision used in the build recipe of the testing environment
+	BOTAN_REV=1872f899716854927ecc68022fac318735be8824
 	BOTAN_DIR=$TRAVIS_BUILD_DIR/../botan
 
 	# if the leak detective is enabled we have to disable threading support
@@ -15,8 +17,10 @@ build_botan()
 	fi
 	# disable some larger modules we don't need for the tests
 	BOTAN_CONFIG="$BOTAN_CONFIG --disable-modules=pkcs11,tls,x509,xmss"
-	git clone --depth 1 https://github.com/randombit/botan.git $BOTAN_DIR &&
+
+	git clone https://github.com/randombit/botan.git $BOTAN_DIR &&
 	cd $BOTAN_DIR &&
+	git checkout $BOTAN_REV &&
 	python ./configure.py --amalgamation $BOTAN_CONFIG &&
 	make -j4 libs >/dev/null &&
 	sudo make install >/dev/null &&