Put prototypes for the functions exported by wcwidth.c in putty.h, and remove

one from terminal.c.  Have wcwidth.c include putty.h to get its prototypes.

[originally from svn r2377]

putty.h

@@ -599,6 +599,12 @@ char *cp_enumerate (int index);
 char *cp_name(int codepage);
 void get_unitab(int codepage, wchar_t * unitab, int ftype);
 
+/*
+ * Exports from wcwidth.c
+ */
+int wcwidth(wchar_t ucs);
+int wcswidth(const wchar_t *pwcs, size_t n);
+
 /*
  * Exports from mscrypto.c
  */