s3:loadparm: prevent infinite include nesting.

s3:loadparm: prevent infinite include nesting.

This introduces a hard coded MAX_INCLUDE_DEPTH of 100.
When this is exceeded, handle_include (and hence lp_load) fails.

One could of course implement a more intelligent loop detection
in the include-tree, but this would require some restructuring
of the internal loadparm housekeeping. Maybe as a second improvement
step.

Michael