Make multiple #line’s update dblines in evals

Make multiple #line’s update dblines in evals

The array-copying stuff that happens when #line 3 "filename" is
encountered in a string eval is not sufficient.  If there are multiple
such statements, only the first one copies the debugger’s lines arrays
(@{"_<filename"}) into the new array.

Checking that CopFILESV(PL_curcop) begins with ‘(eval ’ is a bit
silly, since the parser already knows whether it’s processing a file
without having to check file names.  (And what if you have a real file
beginning with ‘(eval ’?)

See commit 8818d40 and others that it references, for the history of
this piece of code.