[krbdev.mit.edu #8263] db_module_dir doesn't stop modules in install tree from being loaded

[Greg Hudson via RT]

The KDB interface does not use the new plugin framework yet.  The 
location of DB modules can be controlled by the db_module_dir 
variable, which we use in the test suite.

When db_module_dir is set, kdb_load_library() concatenates all values 
of the variable and the hardcoded install-tree path and calls 
krb5int_open_plugin_dirs() on the full list, with a filebases of the 
module name (like "db2").  It then calls 
krb5int_get_plugin_dir_data() to load all modules in all of the named 
directories which match the filebase and contain a 
"kdb_function_table" symbol.  Only the first result is used.

In a typical test suite scenario with a populated install tree, the 
db2.so from the build tree and the db2.so from the install tree will 
both be loaded, but only the build tree module will be used.  
Although this is generally harmless to the tests, anyone 
instrumenting the test suite will see an alarming reference to the 
install tree.

kdb_load_library() should not use the hardcoded pathname if 
db_module_dir is set.