Deprecate svn_fs_revision_prop() and svn_fs_txn_prop()?

[Blair Zajac]

We allow binary data to be stored in revision properties, and given that 
svn_fs_revision_prop() and svn_fs_txn_prop() return const char * data, then it's 
possible for the caller to not "see" all the data if there's a \0 in it.

So should we deprecate them?  Maybe add ...prop2() versions that use 
svn_string_t?
Blair