xbiff-1.0.4-bp156.3.6

- modernize spec file (move license to licensedir)

- Update to version 1.0.4
  * Use _CONST_X_STRING to make libXt declare String as const char *
  * Fix -Wsign-compare warning in quit() function
  * Clarify how volume works
  * autogen.sh: use exec instead of waiting for configure to finish
  * autogen.sh: Honor NOCONFIGURE=1
  * autogen.sh: use quoted string variables
  * autogen: add default patch prefix
  * Update configure.ac bug URL for gitlab migration
  * configure: Drop AM_MAINTAINER_MODE
  * Update README for gitlab migration

- Split xbiff from xorg-x11. Initial version: 1.0.3.