Fix port-acorn32/15850: machdep.booted_kernel on acorn32 is incorrect.

This has been on my TODO list for some time and i found it time to fix it
since its pretty simple to do.

The patch checks if the kernel is booted from the `UnixFS' RISC OS filing
system (case unimportant) and if so interprets its name to get the unix
file name the kernel has. If it doesn't see this prefix it will asume its
just called `netbsd'

sys/arch/acorn32/stand/BtNetBSD/pling.BtNetBSD/BtNetBSD

@@ -1,5 +1,5 @@
 REM > BtNetBSD
-REM $NetBSD: BtNetBSD,v 1.3 2002/02/11 19:00:07 reinoud Exp $
+REM $NetBSD: BtNetBSD,v 1.4 2002/03/10 01:28:19 reinoud Exp $
 REM
 REM Copyright (c) 2000, 2001, 2002 Reinoud Zandijk
 REM Copyright (c) 1998, 1999, 2000 Ben Harris
@@ -78,6 +78,14 @@ REM get kernel name
 file$ = LEFT$(args$, INSTR(args$, " ")-1)
 PRINT"Booting ";file$;" ";args$''
 
+
+IF FNtolower(LEFT$(file$,9))="unixfs:$." THEN
+  kernelname$=MID$(file$, 10)
+ELSE
+  kernelname$="netbsd" : REM RISC OS file namen zeggen niets XXX
+ENDIF
+
+
 REM Get some space to mess with
 REM   Declare a large array ... and then wipe it/map it in in the OS_Mem loop
 REM   the difference is that RO4 won't map it in by default and
@@ -671,7 +679,7 @@ DEF PROCnew_configuration_structure
     ; u_char machine_id[4]
         EQUD          machineId%
     ; char kernelname[80]
-        EQUS          LEFT$(file$+CHR$0+STRING$(80, " "), 80)
+        EQUS          LEFT$(kernelname$+CHR$0+STRING$(80, " "), 80)
     ; char args[512]
         EQUS          args$+CHR$0
         ]: P% += 512 - LEN(args$+CHR$0): [ OPT opt%
@@ -810,7 +818,7 @@ DEF PROCold_configuration_structure
     ;vrampages%
         EQUD          totalvrampages%
     ;kernelname%
-        EQUS          LEFT$(file$+CHR$0+STRING$(80, " "), 80)
+        EQUS          LEFT$(kernelname$+CHR$0+STRING$(80, " "), 80)
     ;framerate%
         EQUD          56 ; XXXXX
     ;machine_id%
@@ -1250,3 +1258,17 @@ DEF FNvdu_var(var%)
 
 DEF FNroundup(val%, size%)
 =val% + (size% - 1) AND NOT (size% - 1)
+
+
+DEF FNtolower(name$)
+  LOCAL A$, Ch$, i%
+  FOR i%=1 TO LEN(name$)
+    Ch$ = LEFT$(name$,1)
+    IF Ch$>="A" AND Ch$<="Z" THEN
+      A$ += CHR$(ASC(Ch$)+ASC("a")-ASC("A"))
+    ELSE
+      A$ += Ch$
+    ENDIF
+    name$ = MID$(name$, 2)
+  NEXT
+= A$