Revision 396031

XSP block: Fix regression introduced in 2.1.8 that under specific circumstances logicsheets
were not applied, leading to compilation errors.  This manifested itself only if
a) two XSPs referred to the same custom logicsheet by a relative location path,
b) the custom logicsheet used another logicsheet, and
c) the built-in logicsheet's namespace was not mentioned in xsp:page.
The compilation errors occurred always when calling the second XSP for the first time.
Fix also race condition which could lead to similar XSP compilation errors under high load
when accessing the same logicsheet for the first time.