Make Subversion a bit more friendly to use in very restricted Windows user
scenarios: fix usage of our libraries in environments without a user profile.

This avoids a 20-30 second delay for each invocation in this use case, where
we used to try creating a default config in a directory where we are not
allowed to write.

* subversion/libsvn_subr/config_file.c
  (svn_config__sys_config_path): Update caller.
  (svn_config_get_user_config_path): Handle no homedir on Windows, like on
    other platforms.

* subversion/libsvn_subr/config_impl.h
  (svn_config__win_config_path): Update prototype.

* subversion/libsvn_subr/config_win.c
  (includes): Move include to start of file.
  (svn_config__win_config_path): Update prototype. Verify if we have a real
    profile. Properly canonicalize the returned path to our internal style.
  (SVN_REG_DEFAULT_NAME_SIZE): Update outdated comment. I think we fixed our
    stringbuffer class to work on any platform now.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1546814 13f79535-47bb-0310-9956-ffa450edef68