Allow 'svn merge' to merge diffs which add 'svn:eol-style' properties

Allow 'svn merge' to merge diffs which add 'svn:eol-style' properties
to files that used to have inconsistent newlines.

Specifically, if the diff being applied adds an 'svn:eol-style'
property to a file, then the left file gets converted to the new EOL
style before running diff3.  If that left file (ie, an old repository
file) had inconsistent newlines, then svn errored out with a useless
"svn: File '/tmp/tmp' has inconsistent newlines", and there was
basically no recourse.  So let it repair newlines.

* subversion/libsvn_wc/merge.c
  (maybe_update_target_eols): Repair newlines when translating 'left'
   file in a merge.

git-svn-id: http://svn.collab.net/repos/svn/trunk@30756 612f8ebc-c883-4be0-9ee0-a4e9ef946e3a