Do not allow a dumped Emacs to be dumped

diff --cc src/ChangeLog
index d2572e7,d2572e7..fa6d265
--- 1/src/ChangeLog
--- 2/src/ChangeLog
+++ b/src/ChangeLog
@@@ -1,3 -1,3 +1,12 @@@
++2014-03-21  Daniel Colascione  <dancol@dancol.org>
++
++      Always prohibit dumping a dumped Emacs.
++
++      * emacs.c (might_dump): New variable.
++      (Fdump_emacs): Always prohibit dumping of dumped Emacs.
++      * lisp.h (might_dump): Declare.
++      * unexcw.c (unexec): Remove now-redundant multiple-dump detection code.
++
  2014-03-20  Paul Eggert  <eggert@cs.ucla.edu>
  
        * doc.c (store_function_docstring): Fix pointer signedness mismatch.

diff --cc src/emacs.c
index fd93324,fd93324..3f0d3c4
--- 1/src/emacs.c
--- 2/src/emacs.c
+++ b/src/emacs.c
@@@ -121,6 -121,6 +121,9 @@@ Lisp_Object Vlibrary_cache
     on subsequent starts.  */
  bool initialized;
  
++/* Set to true if this instance of Emacs might dump.  */
++bool might_dump;
++
  #ifdef DARWIN_OS
  extern void unexec_init_emacs_zone (void);
  #endif
@@@ -1631,6 -1631,6 +1634,10 @@@ Using an Emacs configured with --with-x
  #endif
  #endif
  
++#ifndef CANNOT_DUMP
++  might_dump = !initialized;
++#endif
++
    initialized = 1;
  
  #ifdef LOCALTIME_CACHE
@@@ -2082,6 -2082,6 +2089,9 @@@ You must run Emacs in batch mode in ord
    if (! noninteractive)
      error ("Dumping Emacs works only in batch mode");
  
++  if (!might_dump)
++    error ("Emacs can be dumped only once");
++
  #ifdef GNU_LINUX
  
    /* Warn if the gap between BSS end and heap start is larger than this.  */

diff --cc src/lisp.h
index 2f9a30f,2f9a30f..df8f312
--- 1/src/lisp.h
--- 2/src/lisp.h
+++ b/src/lisp.h
@@@ -800,6 -800,6 +800,7 @@@ extern _Noreturn Lisp_Object wrong_type
  
  /* Defined in emacs.c.  */
  extern bool initialized;
++extern bool might_dump;
  
  /* Defined in eval.c.  */
  extern Lisp_Object Qautoload;

diff --cc src/unexcw.c
index fcca5e5,fcca5e5..25d13ca
--- 1/src/unexcw.c
--- 2/src/unexcw.c
+++ b/src/unexcw.c
@@@ -286,13 -286,13 +286,6 @@@ unexec (const char *outfile, const cha
    int ret;
    int ret2;
  
--  if (bss_sbrk_did_unexec)
--    {
--      /* can only dump once */
--      printf ("You can only dump Emacs once on this platform.\n");
--      return;
--    }
--
    report_sheap_usage (1);
  
    infile = add_exe_suffix_if_necessary (infile, infile_buffer);