This bug would cause multiple errors when building the documentation of Git,
for example, like:
error : xmlAddEntity: invalid redeclaration of predefined entity
* gnu/packages/patches/docbook2x-entity-lt.patch: New file.
* gnu/local.mk (dist_patch_DATA): Register it.
* gnu/packages/docbook.scm (docbook2x) [source]: Apply it.
Change-Id: I8d2e694ff4b97a1016644d3525b2cddb1b85f12d
