configure.ac: try to guess real svn revision if any
configure.ac: try to guess real svn revision if any

mrmichalis/libtorrent-code,mrmichalis/libtorrent-code,mildred/rasterbar-libtorrent,mildred/rasterbar-libtorrent,mrmichalis/libtorrent-code,mildred/rasterbar-libtorrent,mildred/rasterbar-libtorrent,mrmichalis/libtorrent-code,mrmichalis/libtorrent-code,mildred/rasterbar-libtorrent,mrmichalis/libtorrent-code,mildred/rasterbar-libtorrent