Documented os.fsync and os.fdatasync. Closes SF bug 584695.

Doc/lib/libos.tex

@@ -399,6 +399,12 @@ first if necessary.
 Availability: \UNIX, Windows.
 \end{funcdesc}
 
+\begin{funcdesc}{fdatasync}{fd}
+Force write of file with filedescriptor \var{fd} to disk.
+Does not force update of metadata.
+Availability: \UNIX.
+\end{funcdesc}
+
 \begin{funcdesc}{fpathconf}{fd, name}
 Return system configuration information relevant to an open file.
 \var{name} specifies the configuration value to retrieve; it may be a
@@ -429,6 +435,11 @@ with file descriptor \var{fd}, like \function{statvfs()}.
 Availability: \UNIX.
 \end{funcdesc}
 
+\begin{funcdesc}{fsync}{fd}
+Force write of file with filedescriptor \var{fd} to disk.
+Availability: \UNIX.
+\end{funcdesc}
+
 \begin{funcdesc}{ftruncate}{fd, length}
 Truncate the file corresponding to file descriptor \var{fd},
 so that it is at most \var{length} bytes in size.