Rename various shared library functions

Some of the more generically named functions are at risk of colliding
with functions defined in other libraries. To mitigate that risk,
prefix with "repmgr_", unless the name already has some reference
to repmgr.

This requires an extension version bump.

RM20471.

Makefile.in

@@ -27,7 +27,9 @@ DATA = \
   repmgr--5.0--5.1.sql \
   repmgr--5.1.sql \
   repmgr--5.1--5.2.sql \
-  repmgr--5.2.sql
+  repmgr--5.2.sql \
+  repmgr--5.2--5.3.sql \
+  repmgr--5.3.sql
 
 REGRESS = repmgr_extension