Merge branch 'en/xdiff-cleanup'

Merge branch 'en/xdiff-cleanup'

A lot of code clean-up of xdiff.
Split out of a larger topic.

* en/xdiff-cleanup:
  xdiff: change type of xdfile_t.changed from char to bool
  xdiff: add macros DISCARD(0), KEEP(1), INVESTIGATE(2) in xprepare.c
  xdiff: rename rchg -> changed in xdfile_t
  xdiff: delete chastore from xdfile_t
  xdiff: delete fields ha, line, size in xdlclass_t in favor of an xrecord_t
  xdiff: delete redundant array xdfile_t.ha
  xdiff: delete struct diffdata_t
  xdiff: delete local variables that alias fields in xrecord_t
  xdiff: delete superfluous function xdl_get_rec() in xemit
  xdiff: delete unnecessary fields from xrecord_t and xdfile_t
  xdiff: delete local variables and initialize/free xdfile_t directly
  xdiff: delete static forward declarations in xprepare