recognize and execute dynamically linked executables

. generalize libexec slightly to get some more necessary information
	  from ELF files, e.g. the interpreter
	. execute dynamically linked executables when exec()ed by VFS
	. switch to netbsd variant of elf32.h exclusively, solves some
	  conflicting headers

kernel/arch/i386/pre_init.c

@@ -369,6 +369,7 @@ static void mb_extract_image(multiboot_info_t mbi)
 
 	/* Save memory map for kernel tasks */
 	r = read_header_elf((const char *)MULTIBOOT_KERNEL_ADDR,
+				4096, /* everything is there */
 			    &text_vaddr, &text_paddr,
 			    &text_filebytes, &text_membytes,
 			    &data_vaddr, &data_paddr,
@@ -401,6 +402,7 @@ static void mb_extract_image(multiboot_info_t mbi)
 	/* Load boot image services into memory and save memory map */
 	for (i = 0; module < &mb_module_info[mods_count]; ++module, ++i) {
 	    r = read_header_elf((const char *)module->mod_start,
+				module->mod_end - module->mod_start + 1,
 				&text_vaddr, &text_paddr,
 				&text_filebytes, &text_membytes,
 				&data_vaddr, &data_paddr,