pgsql: Now that the shared library name can be adjusted in the library

Now that the shared library name can be adjusted in the library test,
have pg_upgrade allocate a maximum fixed size buffer for testing the
library file name, rather than base the allocation on the library name.

Backpatch to 9.1.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/6d5aae7afacc564ead2af88c76b13cfc55750556

Modified Files
--------------
contrib/pg_upgrade/function.c | 3 +--
1 files changed, 1 insertions(+), 2 deletions(-)