Treat unsupported WC formats as "unknown" rather than raising an error.
Many tests currently fail on the 1.7.x branch if run within a format 30 (i.e. trunk client) working copy. The most prominent failure is an error from 'svn checkout' which refuses to create a format 29 working copy within a format 30 one, even though the two working copies are suposed to be entirely unrelated.
If this patch is applied to 1.7.x, most tests now pass in a format 30 working copy, except for the following:
FAIL: commit_tests.py 26: commit from two working copies FAIL: special_tests.py 19: operate on symlink to wc FAIL: special_tests.py 20: svnversion on symlink to wc FAIL: stat_tests.py 19: status on unversioned dir
* subversion/libsvn_wc/lock.c (svn_wc__internal_check_wc): If the format isn't supported, just return a format number of zero, rather than raising an error indicating that the working copy is not supported.