tidy: xrdopt. (#364)

* Remove unused `print_lispusage()`.
* Make some globals into function locals.
* Make the options table into a `static`. It can't be `const`
  because `XrmParseCommand` wants a mutable pointer.
* Remove unused `homeDB`.
* Stop using `caddr_t`, use `XPointer`. `caddr_t` is not POSIX
  and never made it past old obsolete BSD code.

inc/xrdoptdefs.h

@@ -1,6 +1,5 @@
 #ifndef XRDOPTDEFS_H
 #define XRDOPTDEFS_H 1
 void print_Xusage(const char *prog);
-void print_lispusage(const char *prog);
 void read_Xoption(int *argc, char *argv[]);
 #endif