common: Cleanup the use of USE_NPTH and HAVE_NPTH macros.

* configure.ac (HAVE_NPTH): New ac_define.
* common/estream.c: Use USE_NPTH instead of HAVE_NPTH.
* common/http.c: Ditto.  Replace remaining calls to pth by npth calls.
(connect_server): Remove useless _().
* common/exechelp-posix.c, common/exechelp-w32.c
* common/exechelp-w32ce.c: Use HAVE_PTH to include npth.h.
* common/init.c (_init_common_subsystems): Remove call to pth_init.
* common/sysutils.c (gnupg_sleep): Use npth_sleep.
* scd/ccid-driver.c (my_sleep): Ditto.
--

USE_NPTH is used in case were we may build with and without nPth.  The
missing definition HAVE_NPTH didn't allowed us to build outher sources
with nPTh support.

configure.ac

@@ -900,9 +900,10 @@ AC_DEFINE_UNQUOTED(SHRED,
 #
 AM_PATH_NPTH("$NEED_NPTH_API:$NEED_NPTH_VERSION",have_npth=yes,have_npth=no)
 if test "$have_npth" = "yes"; then
-  # We define this macro because some code parts require it.
-  AC_DEFINE(USE_NPTH, 1,
+  AC_DEFINE(HAVE_NPTH, 1,
               [Defined if the New Portable Thread Library is available])
+  AC_DEFINE(USE_NPTH, 1,
+              [Defined if support for nPth is requested and nPth is available])
 else
   AC_MSG_WARN([[
 ***