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/tgi/a2.hi.s

@@ -83,7 +83,10 @@ Y2      :=      ptr4
 
         .byte   $74, $67, $69   ; "tgi"
         .byte   TGI_API_VERSION ; TGI API version number
+
+libref:
         .addr   $0000           ; Library reference
+
         .word   280             ; X resolution
         .word   192             ; Y resolution
         .byte   8               ; Number of drawing colors
@@ -120,6 +123,10 @@ pages:  .byte   2               ; Number of screens available
 
         .bss
 
+.ifndef __APPLE2ENH__
+machinetype: .res 1
+.endif
+
 ; Absolute variables used in the code
 
 ERROR:  .res    1               ; Error code
@@ -146,13 +153,22 @@ FONT:
 ; most of the time.
 ; Must set an error code: NO
 INSTALL:
-        .ifdef  __APPLE2ENH__
+        .ifndef __APPLE2ENH__
+        lda     libref
+        ldx     libref+1
+        sta     ptr1
+        stx     ptr1+1
+        ldy     #$0
+        lda     (ptr1),y
+        sta     machinetype
+        bpl     :+
+        .endif
         ; No page switching if 80 column store is enabled
         bit     RD80COL
         bpl     :+
         lda     #$01
         sta     pages
-:       .endif
+:
 
         ; Fall through
 
@@ -175,10 +191,16 @@ INIT:
         ; Switch into graphics mode
         bit     MIXCLR
         bit     HIRES
-        .ifdef  __APPLE2ENH__
+
+        .ifndef __APPLE2ENH__
+        bit     machinetype
+        bpl     clr_txt
+        .endif
+
         sta     IOUDISON
         bit     DHIRESOFF
-        .endif
+
+clr_txt:
         bit     TXTCLR
 
         ; Beagle Bros Shape Mechanic fonts don't
@@ -200,11 +222,14 @@ DONE:
         bit     TXTSET
         bit     LOWSCR
 
-        .ifdef  __APPLE2ENH__
+        .ifndef __APPLE2ENH__
+        bit     machinetype
+        bpl     reset_wndtop
+        .endif
         ; Limit SET80COL-HISCR to text
         bit     LORES
-        .endif
 
+reset_wndtop:
         ; Reset the text window top
         lda     #$00
         sta     WNDTOP