fix various descriptions of "ctime"

(closes SF patch #870287)

Doc/lib/libos.tex

@@ -909,7 +909,8 @@ the \ctype{stat} structure, namely:
 \member{st_atime} (time of most recent access),
 \member{st_mtime} (time of most recent content modification),
 \member{st_ctime}
-(time of most recent content modification or metadata change).
+(platform dependent; time of most recent metadata change on \UNIX, or
+the time of creation on Windows).
 
 \versionchanged [If \function{stat_float_times} returns true, the time
 values are floats, measuring seconds. Fractions of a second may be

Doc/lib/libstat.tex

@@ -110,7 +110,10 @@ Time of last modification.
 \end{datadesc}
 
 \begin{datadesc}{ST_CTIME}
-Time of last status change (see manual pages for details).
+The ``ctime'' as reported by the operating system.  On some systems
+(like \UNIX) is the time of the last metadata change, and, on others
+(like Windows), is the creation time (see platform documentation for
+details).
 \end{datadesc}
 
 The interpretation of ``file size'' changes according to the file