2011-05-11  Ryan Johnson  <ryan.johnson@cs.utoronto.ca>

	* child_info.h (fork_api_fatal): new macro for reporting to the
	parent of a forked child that the fork cannot continue.
	* fork.cc (frok::child): check for clobbered DLL_LOAD early while
	we can still retry. Exit cleanly and report to parent if fork
	failed for well-known reasons (clobbered address space). Also, set
	in_forkee=false at end of fork even if no DLL_LOAD are present.
	(fork): sort the dll list topologically before forking. When the
	child loads each dll, all dependencies are already loaded and will
	no longer risk being pulled in unexpectedly.
	* heap.cc (heap_init): use fork_api_fatal for clean exit/retry of
	failed fork.
	* pinfo.h: define new EXITCODE_FORK_FAILED to aid clean exit/retry
	of failed forks.
	* sigproc.cc (child_info::proc_retry): see above.
	(child_info_fork::handle_failure): ditto.
	* dll_init.cc (dll_list::find_by_modname): new function to search
	the dll list for a module name only (no path).
	(dll_list::alloc): added code which aborts a fork attempt if
	DLL_LINK dlls landed at the wrong base address in the child. Also,
	initialize newly-added members of the dll class.
	(dll_list::topsort, dll_list::topsort_visit): new functions to
	sort the dll list topologically by dependencies
	(dll_list::append): new function to factor out the append
	operation (used by dll_list::topsort)
	(dll_list::populate_deps): new function to identify dll dependencies
	(dll_list::block_bad_address_space): new function to reserve all
	free space in the low 4MB. Reduces somewhat the probability of a
	dynamic dll clashing with windows heaps or thread stacks.
	(reserve_upto, release_upto): removed (buggy, no longer needed)
	(reserve_at): no longer reserves space needed by the target dll if
	the latter overlaps the free region to be blocked.
	(dll_list::reserve_space): new function to reserve all space
	needed by DLL_LOAD dlls early in the fork process.
	(dll_list::load_after_fork): rewritten. New version uses recursion
	to track reservations it makes while trying to make dlls land
	where they belong. No longer set in_forkee=false (now done in
	fork.cc)
	* dll_init.h (dll_list, dll): added new class members to support
	topsort and other improvements to forking. No longer run dtors if
	in_forkee is true.
	(pefile): New class allowing simple introspection of dll images.
	* dcrt0.cc (dll_crt0_1): call dll_list::block_bad_address_space