i386: new stub strategy to avoid problems with early mmap layout

The stub occupies the same region that execve() would create
for the original progam.  The stub copies everything to a new area,
erases the original region, replaces it with the de-compressed
program, and erases the copy of itself via the escape hatch.
The copy is inexpensive via mmap() of /proc/self/exe.

	modified:   stub/src/i386-linux.elf-entry.S
	modified:   stub/src/i386-linux.elf-fold.S
	modified:   stub/src/i386-linux.elf-main.c

	modified:   p_lx_elf.cpp
	modified:   p_lx_elf.h
	modified:   p_lx_interp.cpp
	modified:   p_lx_interp.h
	modified:   p_lx_sh.cpp
	modified:   p_lx_sh.h
	modified:   p_mach.cpp
	modified:   p_mach.h
	modified:   p_unix.cpp
	modified:   p_unix.h
	modified:   p_vmlinx.cpp

	plus .h, .map, .dump

src/p_unix.h

@@ -55,7 +55,7 @@ protected:
     // called by the generic pack()
     virtual void pack1(OutputFile *, Filter &);  // generate executable header
     virtual int  pack2(OutputFile *, Filter &);  // append compressed data
-    virtual void pack3(OutputFile *, Filter &);  // append loader
+    virtual off_t pack3(OutputFile *, Filter &);  // append loader
     virtual void pack4(OutputFile *, Filter &);  // append PackHeader
 
     virtual void patchLoader() = 0;