build fails on freebsd

FreeBSD does not allow using ```<malloc.h>``` unless -traditional is specified.

```log
gmake[4]: Entering directory `/a/webvtt/src/libwebvtt'
  CC       libwebvtt_la-alloc.lo
In file included from alloc.c:32:
/usr/include/malloc.h:3:2: error: "<malloc.h> has been replaced by <stdlib.h>"
#error "<malloc.h> has been replaced by <stdlib.h>"
 ^
alloc.c:53:10: warning: implicitly declaring library function 'malloc' with type
      'void *(unsigned long)'
  return malloc( nb );
         ^
alloc.c:53:10: note: please include the header <stdlib.h> or explicitly provide a
      declaration for 'malloc'
alloc.c:59:3: warning: implicit declaration of function 'free' is invalid in C99
      [-Wimplicit-function-declaration]
  free( ptr );
  ^
2 warnings and 1 error generated.
```

```diff
diff --git a/src/libwebvtt/alloc.c b/src/libwebvtt/alloc.c
index 4e80241..41e1879 100644
--- a/src/libwebvtt/alloc.c
+++ b/src/libwebvtt/alloc.c
@@ -26,11 +26,7 @@
  */
 
 #include <webvtt/util.h>
-#if ( defined(__APPLE__) && defined(__MACH__) )
 #include <stdlib.h>
-#else
-#include <malloc.h>
-#endif
 #include <string.h>
 
 static void *default_alloc( void *unused, webvtt_uint nb );
```

libc++ has ```<tuple>``` while libstdc++ has ```<tr1/tuple>```. And FreeBSD is moving
away from libstdc++-4.2 (GPLv2) as it doesn't support c++11 features.

```log
gmake[3]: Entering directory `/a/webvtt/test/gtest'
  CXX      libgtest_la-gtest-all.lo
In file included from gtest-all.cc:39:
./gtest/gtest.h:1621:13: fatal error: 'tr1/tuple' file not found
#   include <tr1/tuple>  // NOLINT
            ^
1 error generated.
```

To fix just sync with googletest or merge at least [r621](https://code.google.com/p/googletest/source/detail?r=621).