Bug reported to the Debian BTS recently by Arnaud Giersch.
The third parameter (Bool override) is missing in the manual page for
XrmCombineDatabase (XrmMergeDatabases(3X11)). It should be:
void XrmCombineDatabase(XrmDatabase source_db, XrmDatabase *target_db,
Sorry about the phenomenal bug spam, guys. Adding xorg-team@ to the QA contact so bugs don't get lost in future.
Fixed in 1a18319b3bde08dd9ef69c7cd735a76000cf3177