Actually, it's not "requires" - you can specify which xapian-config to use for the bindings like so:
./configure XAPIAN_CONFIG=/usr/local/bin/xapian-config-1.3
Or to just change the leaf-name to look for on PATH:
./configure XAPIAN_CONFIG=xapian-config-1.3
This is documented in the xapian-bindings' INSTALL file, and also in ./configure --help.
This suffix mismatch is only an issue for development snapshots. For stable releases, we don't add a suffix to the installed xapian-config by default, so we don't want to for here (and when building from git, bootstrap generates a top-level configure script which passes a suitable XAPIAN_CONFIG=X to the sub-configures such that the in-tree version is used).
It would make more sense to default to xapian-config with the appropriate suffix for development versions though, and looking at the git history, we actually did this for 1.1.3 and later: [97e77de910175d60cd8b374033e27b36d7962036] (before 1.1.3, XO_LIB_XAPIAN had a hard-coded default of xapian-config).
That change was correctly reverted in 1.2.0, but we failed to reinstate the equivalent for 1.3.0. I think we need a mechanism which automatically adds the suffix -X.Y for version X.Y.Z if (and only if) Y is odd, so that we didn't have to manually add and remove this at the start and end of each development release series - it's clearly all to easy to fail to do so.
Same issue applies to xapian-omega.
