Define and use a path separator string

A colon can't be used to separate paths on Windows since they are used
in drive sepecification.  Define a macro that can be used as a path
separator string.  On Windows, this is defined as ";".  It is a ":"
everywhere else.

lib/krb5/krb5_locl.h

@@ -188,6 +188,10 @@ struct _krb5_krb_auth_data;
 #define ALLOC(X, N) (X) = calloc((N), sizeof(*(X)))
 #define ALLOC_SEQ(X, N) do { (X)->len = (N); ALLOC((X)->val, (N)); } while(0)
 
+#ifndef PATH_SEP
+#define PATH_SEP ":"
+#endif
+
 /* should this be public? */
 #define KEYTAB_DEFAULT "FILE:" SYSCONFDIR "/krb5.keytab"
 #define KEYTAB_DEFAULT_MODIFY "FILE:" SYSCONFDIR "/krb5.keytab"