* configure.ac (SEPCONSTANTS): New to define DIRSEP_C et al.
* w32-util.c (read_w32_registry_string): Updated from code used by
GnuPG.  This allows for expanding strings and features the
implicit fallback key.
(w32_shgetfolderpath, find_program_at_standard_place): New.
(_gpgme_get_gpg_path, _gpgme_get_gpgsm_path): With no registry
entry, locate the programs at the standard place.
(dlopen, dlsym, dlclose): New, so that we can keep on using what
we are accustomed to.
* debug.c (debug_init): Use PATHSEP_C so that under W32 a
semicolon is used which allows us to create files with drive
letters.
* w32-io.c (_gpgme_io_read, _gpgme_io_write): Print content in
debug mode too.