[TxMt] Fix for subversion log error

[Noah M. Daniels]

I'd just started using the Subversion bundle, and everything was  
working great once I defined $TM_SVN except for the Log command,  
which would complain that it couldn't find the svn binary.

Turns out that the problem is within the format_log.rb program; the  
line defining $svn_url read as follows:

$svn_url = `svn info #{ENV['PWD'].quote_filename_for_shell}|grep URL| 
cut -b6-`.chop

changing it to:

$svn_url = `#{ENV['TM_SVN']} info #{ENV 
['PWD'].quote_filename_for_shell}|grep URL|cut -b6-`.chop

corrects the problem.