Fix a "dereference of type-punned pointer" compiler warning

gcc (4.4.0) issues the following warning:

    src/revobject.c:33: warning: dereferencing type-punned pointer \
        will break strict-aliasing rules

We suppress the warning by copying the first 4 bytes from the oid
structure into an 'unsigned int' using memcpy(). This will also
fix any potential alignment issues on certain platforms.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Andreas Ericsson <ae@op5.se>

src/revobject.c

@@ -30,7 +30,9 @@ static const double max_load_factor = 0.65;
 
 static unsigned int git_revpool_table__hash(const git_oid *id)
 {
-	return *((unsigned int *)id->id);
+	unsigned int r;
+	memcpy(&r, id->id, sizeof(r));
+	return r;
 }
 
 git_revpool_table *git_revpool_table_create(unsigned int min_size)