Prefer pointer types in prefix operator parsing

[iflan]

This fixes issue #49 in the simplest way. Before, if the dereferenced variable was a byte type, the result of the word pointer dereference operator, *, would be a byte type. This caused *@a to return a byte if a was a byte type. Now the pointer type is used instead, causing *@a to return a word.

Prefix operator parsing allows some nonsensical constructions, like @*x, but these were already possible before.

Before the output from:

include "inc/cmdsys.plh"

byte a
byte b
word x

a = 5
b = 6
x = $55FF
puti(*@a) // 5
putln()
puti(*(@a)) // 1541
putln()
puti(@*a) // 5
putln()
puti(^@x) // 255
putln()
puti(^(@x)) // 255
putln()
puti(@^x) // 255
putln()
done

was:

5
1541
5
255
255
255

now it is:

1541
1541
1541
255
255
255

[dschmenk]

Thanks!