So subject say it all. I have install postgis 2.0.3 and 2.1.0beta3dev on my postgresql 9.2.4 server. I had to make some changes to support some changes in 2.1.0 and we are good on both versions.
On postgis 2.1.0 they have changed all the function names to st_camelCaseFunctionName() from the older style st_camel_case_function_name() names and the old names work be an annoying NOTICE message is emitted that broke or tests.
So I have added a utility function pgr_versionLess(v1, v2) function that can be used like:
if pgr_versionLess(postgis_lib_version(), '2.1') then
-- use old style names
else
-- use new style names
end if;
Keep this in mind when you write your wrapper code if you need to support multiple version.
-Steve