Correct argument specifications of load_compiled and load_source: the file

argument is optional on both (the format string is "ss|O!").

Doc/lib/libimp.tex

@@ -192,7 +192,7 @@ Return \code{True} if there is a frozen module (see
 no such module.
 \end{funcdesc}
 
-\begin{funcdesc}{load_compiled}{name, pathname, file}
+\begin{funcdesc}{load_compiled}{name, pathname, \optional{file}}
 \indexii{file}{byte-code}
 Load and initialize a module implemented as a byte-compiled code file
 and return its module object.  If the module was already initialized,
@@ -218,7 +218,7 @@ shared libraries is highly system dependent, and not all systems
 support it.)
 \end{funcdesc}
 
-\begin{funcdesc}{load_source}{name, pathname, file}
+\begin{funcdesc}{load_source}{name, pathname\optional{, file}}
 Load and initialize a module implemented as a Python source file and
 return its module object.  If the module was already initialized, it
 will be initialized \emph{again}.  The \var{name} argument is used to