Make new event trigger facility actually do something.

Commit 3855968f32 added syntax, pg_dump,
psql support, and documentation, but the triggers didn't actually fire.
With this commit, they now do.  This is still a pretty basic facility
overall because event triggers do not get a whole lot of information
about what the user is trying to do unless you write them in C; and
there's still no option to fire them anywhere except at the very
beginning of the execution sequence, but it's better than nothing,
and a good building block for future work.

Along the way, add a regression test for ALTER LARGE OBJECT, since
testing of event triggers reveals that we haven't got one.

Dimitri Fontaine and Robert Haas

src/include/port.h

@@ -443,6 +443,7 @@ extern int pqGethostbyname(const char *name,
 
 extern void pg_qsort(void *base, size_t nel, size_t elsize,
 		 int (*cmp) (const void *, const void *));
+extern int pg_qsort_strcmp(const void *a, const void *b);
 
 #define qsort(a,b,c,d) pg_qsort(a,b,c,d)