Apple2: Make 80-columns support dynamic on apple2 target

Add a machinetype identifier to help us quickly identify
Apple //e (bit 7) and //e enhanced (bit 6).

Use it in conio functions for 80-columns code instead of
relying entirely on the __APPLE2ENH__ target.

Move videomode() to the apple2 target, and have it return
an error if 80-columns hardware is not available - this
is a lie for now, it is considered available on //e enhanced,
which may not be true, and not available on //e, which
may also be not true. An ulterior patch will make that
check correctly.

Adapt the box/line drawing characters so that one can use
MouseText on the apple2 target if it is available, by
defining DYN_DRAW_BOX. No change by default: MouseText is
considered available on apple2enh and not available on
apple2.

libsrc/apple2/mcbdefault.s

@@ -9,6 +9,10 @@
 
         .export         _mouse_def_callbacks
 
+        .ifndef __APPLE2ENH__
+        .import         machinetype
+        .endif
+
         .include        "apple2.inc"
 
 ; ------------------------------------------------------------------------
@@ -42,11 +46,14 @@ cursor = '+' | $40              ; Flashing crosshair
         .endif
 
 getcursor:
-        .ifdef  __APPLE2ENH__
+        .ifndef __APPLE2ENH__
+        bit     machinetype
+        bpl     column
+        .endif
         bit     RD80VID         ; In 80 column mode?
         bpl     column          ; No, skip bank switching
 switch: bit     LOWSCR          ; Patched at runtime
-        .endif
+
 column: ldx     #$00            ; Patched at runtime
 getscr: lda     $0400,x         ; Patched at runtime
         cmp     #cursor
@@ -55,9 +62,7 @@ getscr: lda     $0400,x         ; Patched at runtime
 setcursor:
         lda     #cursor
 setscr: sta     $0400,x         ; Patched at runtime
-        .ifdef  __APPLE2ENH__
         bit     LOWSCR          ; Doesn't hurt in 40 column mode
-        .endif
         rts
 
 ; ------------------------------------------------------------------------
@@ -65,9 +70,7 @@ setscr: sta     $0400,x         ; Patched at runtime
         .code
 
 done:
-        .ifdef  __APPLE2ENH__
         bit     LOWSCR          ; Doesn't hurt in 40 column mode
-        .endif
 return: rts
 
 ; Hide the mouse cursor.
@@ -108,14 +111,14 @@ movex:
         inx
         bcs     :-
         stx     column+1
-        .ifdef  __APPLE2ENH__
+
+        ; Patch switch anyway, it will just be skipped over if in 40-col mode
         adc     #7 / 2          ; Left or right half of 40-col column?
         ldx     #<LOWSCR        ; Columns 1,3,5..79
         bcs     :+
         .assert LOWSCR + 1 = HISCR, error
         inx                     ; Columns 0,2,4..78
 :       stx     switch+1
-        .endif
         rts
 
 ; Move the mouse cursor y position to the value in A/X.