Make valgrind run on travis tests of v8js

Valgrind checks for invalid memory accesses and memory leaks.

"-m" makes php unit tests use valgrind (and malloc instead of emalloc, etc.)

.travis.yml

@@ -8,7 +8,11 @@ php:
 env:
   - V8VER=5.2
   - V8VER=5.1
+  - V8VER=5.2 VALGRIND=1
 
 before_install: make -f Makefile.travis before_install
-install: make -f Makefile.travis install
+install:
+  - if [ "$VALGRIND" = 1 ]; then sudo apt-get install -qq valgrind; export TEST_PHP_ARGS="-m"; fi
+  - make -f Makefile.travis install
+
 script: make -f Makefile.travis test