--debug and infodebug file

[Gavin Smith]

When "info --debug" is used (in the words of the manual),

Before Info's full-screen output is initialized, debugging output
     goes to standard error.  After it is initialized, the debugging
     output is written to the file 'infodebug' in the current working
     directory.

I propose to change this to always writing to standard error. You
would be able to get a complete log by running something like "info
2>infodebug". It would make it less likely that you accidentally
overwrite an existing file called "infodebug". This could be useful
for the test suite where debugging statements could be stored in the
log files.