document wxFileOffset

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@57333 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

interface/wx/filefn.h

@@ -107,6 +107,15 @@ public:
 */
 const int wxInvalidOffset = -1;
 
+/**
+    The type used to store and provide byte offsets or byte sizes for files or streams.
+
+    It is type-defined as @c off_t on POSIX platforms
+    (see http://www.gnu.org/software/libc/manual/html_node/File-Position-Primitive.html)
+    or to @c wxLongLong_t on Windows when @c wxHAS_HUGE_FILES is defined.
+*/
+typedef off_t wxFileOffset;
+
 /**
     Under Unix this macro changes the current process umask to the given value,
     unless it is equal to -1 in which case nothing is done, and restores it to