Bug fix: Fix X pixmap leakage in shadow_paint

- Fix X pixmap leakage in shadow_paint.

- Add the skeleton of a X resource leakage checker.

src/xrescheck.c

@@ -0,0 +1,65 @@
+#include "xrescheck.h"
+
+static xrc_xid_record_t *gs_xid_records = NULL;
+
+#define HASH_ADD_XID(head, xidfield, add) \
+  HASH_ADD(hh, head, xidfield, sizeof(xid), add)
+
+#define HASH_FIND_XID(head, findxid, out) \
+  HASH_FIND(hh, head, findxid, sizeof(xid), out)
+
+#define M_CPY_POS_DATA(prec) \
+  prec->file = file; \
+  prec->func = func; \
+  prec->line = line; \
+
+/**
+ * @brief Add a record of given XID to the allocation table.
+ */
+void
+xrc_add_xid_(XID xid, const char *type, M_POS_DATA_PARAMS) {
+  xrc_xid_record_t *prec = cmalloc(1, xrc_xid_record_t);
+  prec->xid = xid;
+  prec->type = type;
+  M_CPY_POS_DATA(prec);
+
+  HASH_ADD_XID(gs_xid_records, xid, prec);
+}
+
+/**
+ * @brief Delete a record of given XID in the allocation table.
+ */
+void
+xrc_delete_xid_(XID xid, M_POS_DATA_PARAMS) {
+  xrc_xid_record_t *prec = NULL;
+  HASH_FIND_XID(gs_xid_records, &xid, prec);
+  if (!prec) {
+    printf_err("XRC: %s:%d %s(): Can't find XID %#010lx we want to delete.",
+        file, line, func, xid);
+    return;
+  }
+  HASH_DEL(gs_xid_records, prec);
+  free(prec);
+}
+
+/**
+ * @brief Report about issues found in the XID allocation table.
+ */
+void
+xrc_report_xid(void) {
+  for (xrc_xid_record_t *prec = gs_xid_records; prec; prec = prec->hh.next)
+    printf_dbg("XRC: %s:%d %s(): %#010lx (%s) not freed.\n",
+        prec->file, prec->line, prec->func, prec->xid, prec->type);
+}
+
+/**
+ * @brief Clear the XID allocation table.
+ */
+void
+xrc_clear_xid(void) {
+  xrc_xid_record_t *prec = NULL, *ptmp = NULL;
+  HASH_ITER(hh, gs_xid_records, prec, ptmp) {
+    HASH_DEL(gs_xid_records, prec);
+    free(prec);
+  }
+}