[Reduction] #109-113: Signal handling

> "OK, the signal slice is pretty large, let's do it tomorrow"
> stay there for the majority of the day

Oh well, at least it paid off. I *really* should work towards PI loading now,
though.
[Reduction] #114: fperror

OK, one more Borland C function I noticed while I was covering signals.
Change the name of the entry point to STARTX

Because it just so happens that master.lib's bfnt_header structure contains
an element named "START".
And huh, this suddenly works without changing any assembler or linker
parameters? I swear it didn't when I tried it first.
[Reduction] #115: dos_ropen

AKA "fontfile_open()", and originally kept in FONTOPEN.ASM... yeah.
[Reduction] #116: master.lib memory manager variables
[Reduction] #117-118: mem_assign and mem_assign_all
[Reduction] #119: mem_assign_dos

Containing, again, fixes for misreferences in TH04.
[Reduction] #120-122: Heap memory functions

With even more misreferences in switch tables.