Fix usage of _te32/_te64/_te16 for Elf classes

How did it ever work?  UPX_RSIZE_MAX_MEM of 768MiB, Elf32_Off of only
32-bits, and preponderance of little-endian and small positive integers
hides many mis-uses of _te64/_te32.
ELF does not help: e_phnum, e_shnum, Elf32_Section, Elf64_Section are all
16-bit, but sh_info and sh_link are 32-bit.
Templatizing p_elf.h (following the example of p_mach.h) failed
because of complexity.  (Plus too many special cases of ELF where 32-bit
and 64-bit are not parallel.)
	modified:   p_lx_elf.cpp
	modified:   p_lx_sh.cpp
	modified:   p_mach.cpp

src/p_mach.cpp

@@ -1838,7 +1838,7 @@ int PackMachBase<T>::canUnpack()
                 &&  (Mach_header::MH_MAGIC + (sizeof(Addr)>>3)) == uptr[1]) {
                     return true;
                 }
-                unsigned const magic = get_te32(1+ (char const *)uptr);
+                unsigned const magic = get_te32(&uptr[1]);  // FIXME:  probable bug
                 if ((M_NRV2B_8 == method || M_NRV2E_8 == method)
                 && 0xfc==(0xfc & uptr[0])
                 &&  (Mach_header::MH_MAGIC + (sizeof(Addr)>>3)) == magic) {