[merge request] Two librep goodies.

[Teika Kazura <teika lavabit com>]

Hi, I'm glad to annouce these librep patches:
* Important notice
  You have to byte compile all codes again.
* Half way improvement of `debug-on-error' and `backtrace-on-error'
  Previously, setting these values to `t' triggered the debugger /
  the backtrace even if the error is signalled inside of
  `condition-case'. This behavior can be still obtained by setting
  them to a symbol `always'.

  Now, if they're `t', the debugger / the backtrace is invoked only
  if the control is not inside of any `condition-case'. Notice that
  the condition is NOT if the error is actually handled by an error
  handler.

  The default value of `backtrace-on-error' is now `t'.

* When you evaluate a closure, the module to which it belongs is
  printed, too.
  I know spaces around "@" look untidy. But I hope this prevents
  newbies from misunderstanding closure some module is a valid read
  syntax.

* And some doc. Better description on "fluid", which I understand
  for the first time, and "let".

Now by default the backtrace is printed by an error outside of any
condition-case. This is greatlly beneficial. For example, in Sawfish 1.6,
application menu failed for some cases, and it may have really
disappointed some of our lovely Sawfish users, too difficult to find
out the cause. Now they can simply send the backtrace to us.

# Backtrace is not so much informative, but far better than lacking.

Teika (Teika kazura)
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