configure: added --enable-fulldebug to enable extra/expensive debug code.

This is mostly to avoid the allocation required by the externalization of the
transaction dictionary, which in some cases is huge.

This should reduce the massive memory usage required to inspect the externalized
dictionary.

bin/xbps-install/transaction.c

@@ -339,9 +339,11 @@ exec_transaction(struct xbps_handle *xhp, int maxcols, bool yes, bool drun)
 		}
 		goto out;
 	}
+#ifdef FULL_DEBUG
 	xbps_dbg_printf(xhp, "Dictionary before transaction happens:\n");
 	xbps_dbg_printf_append(xhp, "%s",
 	    xbps_dictionary_externalize(xhp->transd));
+#endif
 
 	trans->xhp = xhp;
 	trans->d = xhp->transd;