change tracking:

change tracking:

Better change time handling. Quote from Changes.C:

  Class Change has a changetime field that specifies the exact time at which
  a specific change was made. The change time is used as a guidance for the
  user while editing his document. Presently, it is not considered for LaTeX
  export. To avoid that every keystroke results in a separate change, a
  tolerance interval of 5 minutes is used. That means if there are two adjacent
  changes that only differ in their change time with abs(ct1 - ct2) < 300 sec,
  they will be merged (and the later change time is preserved).
  Technically, the check for equality (or similarity) is made in
  operator==(...). The merging of similar changes happens in method merge().

Resolve FIXMEs for LyX & LaTeX output.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@15569 a592a061-630c-0410-9148-cb99ea01b6c8