Implement newlocale, freelocale, duplocale, uselocale

Add global const __C_locale for reference purposes.

Bump Cygwin API minor number and DLL major version number to 2.6.0.

Signed-off by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/common.din

@@ -381,6 +381,7 @@ dreml= remainderl NOSIGFE
 dup SIGFE
 dup2 SIGFE
 dup3 SIGFE
+duplocale SIGFE
 eaccess = euidaccess SIGFE
 ecvt SIGFE
 ecvtbuf SIGFE
@@ -536,6 +537,7 @@ fread_unlocked SIGFE
 free SIGFE
 freeaddrinfo = cygwin_freeaddrinfo SIGFE
 freeifaddrs SIGFE
+freelocale SIGFE
 fremovexattr SIGFE
 freopen SIGFE
 frexp NOSIGFE
@@ -900,6 +902,7 @@ nanosleep SIGFE
 nearbyint NOSIGFE
 nearbyintf NOSIGFE
 nearbyintl NOSIGFE
+newlocale SIGFE
 nextafter NOSIGFE
 nextafterf NOSIGFE
 nextafterl NOSIGFE
@@ -1417,6 +1420,7 @@ unlockpt NOSIGFE
 unsetenv SIGFE
 updwtmp SIGFE
 updwtmpx SIGFE
+uselocale SIGFE
 usleep SIGFE
 utime SIGFE
 utimensat SIGFE

winsup/cygwin/include/cygwin/version.h

@@ -10,8 +10,8 @@ details. */
    the Cygwin shared library".  This version is used to track important
    changes to the DLL and is mainly informative in nature. */
 
-#define CYGWIN_VERSION_DLL_MAJOR 2005
-#define CYGWIN_VERSION_DLL_MINOR 3
+#define CYGWIN_VERSION_DLL_MAJOR 2006
+#define CYGWIN_VERSION_DLL_MINOR 0
 
 /* Major numbers before CYGWIN_VERSION_DLL_EPOCH are incompatible. */
 
@@ -454,12 +454,13 @@ details. */
        nexttowardf, nexttowardl, pow10l, powl, remainderl, remquol, roundl,
        scalbl, scalblnl, scalbnl, sincosl, sinhl, sinl, tanhl, tanl,
        tgammal, truncl.
+  298: newlocale, freelocale, duplocale, uselocale.
 
   Note that we forgot to bump the api for ualarm, strtoll, strtoull,
   sigaltstack, sethostname. */
 
 #define CYGWIN_VERSION_API_MAJOR 0
-#define CYGWIN_VERSION_API_MINOR 297
+#define CYGWIN_VERSION_API_MINOR 298
 
 /* There is also a compatibity version number associated with the shared memory
    regions.  It is incremented when incompatible changes are made to the shared