Fix a bug where global precompiled code (A) called from a precompiled
procedure causes the core to recompile (A), triggering the trap laid
inside, i.e. 'error "called a copy of compiled code"'.

<pre>Example
----------------------ex1.tcl
proc init {} {
    source ex2.tcl
}
init
----------------------ex2.tcl
puts a
----------------------</pre>

When run as precompiled code the 'puts a' is not executed, only the trap.

Fixed by enclosing the offending code into a guard which prevents its
execution for precompiled code. The change passes the entire testsuite.