isalpha Method
Purpose:
Checks a string for characters outsize the range a-z A-Z
Syntax:
isalpha(string)
Comments:
Returns zero if string is valid. Returns -1 if invalid.
Example:
p instr("abc","b")
p isalpha("abc")
0
p isalpha("abA3")
-1 // fails because of the 3 in the string