Description: Rebuild needed.

Additional info:

Upgraded postgres 9.0.4-4 -> 9.1.1-2

Steps to reproduce:

$ sudo -u postgres pg_upgrade -d /var/lib/postgres-old/data -D /var/lib/postgres/data -b /tmp/usr/bin/ -B /usr/bin
Performing Consistency Checks
-----------------------------
Checking current, bin, and data directories ok
Checking cluster versions ok
Checking database user is a superuser ok
Checking for prepared transactions ok
Checking for reg* system oid user data types ok
Checking for contrib/isn with bigint-passing mismatch ok
Creating catalog dump ok
Checking for prepared transactions ok
Checking for presence of required libraries fatal

| Your installation references loadable libraries that are missing
| from the new installation. You can add these libraries to
| the new installation, or remove the functions using them
| from the old installation. A list of the problem libraries
| is in the file
| "/tmp/loadable_libraries.txt".

Failure, exiting

$ cat /tmp/loadable_libraries.txt
Failed to load library: $libdir/postgis-1.5
ERROR: no se pudo cargar la biblioteca «/usr/lib/postgresql/postgis-1.5.so»: /usr/lib/postgresql/postgis-1.5.so: undefined symbol: DirectFunctionCall4

Rebuilt postgis and the issue went away.