get_{program_,}line() now returns a pike_string.

store_linenumber() is now wide string safe.
Added some more debug to store_linenumber().
Fixes [bug 1866].

Rev: src/builtin.cmod:1.59
Rev: src/builtin_functions.c:1.394
Rev: src/gc.c:1.169
Rev: src/interpret.c:1.219
Rev: src/interpreter.h:1.68
Rev: src/object.c:1.179
Rev: src/opcodes.c:1.113
Rev: src/program.c:1.353
Rev: src/program.h:1.138