Fix buffer overflow on particularly named files and clarify documentation about

output file naming.

Patch by Tsunakawa, Takayuki <tsunakawa.takay@jp.fujitsu.com>

doc/src/sgml/ref/ecpg-ref.sgml

@@ -42,11 +42,9 @@ PostgreSQL documentation
   <para>
    <command>ecpg</command> will convert each input file given on the
    command line to the corresponding C output file.  Input files
-   preferably have the extension <filename>.pgc</filename>, in which
-   case the extension will be replaced by <filename>.c</filename> to
-   determine the output file name.  If the extension of the input file
-   is not <filename>.pgc</filename>, then the output file name is
-   computed by appending <literal>.c</literal> to the full file name.
+   preferably have the extension <filename>.pgc</filename>.
+   The extension will be replaced by <filename>.c</filename> to
+   determine the output file name.
    The output file name can also be overridden using the
    <option>-o</option> option.
   </para>

src/interfaces/ecpg/preproc/ecpg.c

@@ -313,7 +313,8 @@ main(int argc, char *const argv[])
 					base_yyout = stdout;
 				else
 				{
-					output_filename = mm_strdup(input_filename);
+					output_filename = mm_alloc(strlen(input_filename) + 3);
+					strcpy(output_filename, input_filename);
 
 					ptr2ext = strrchr(output_filename, '.');
 					/* make extension = .c resp. .h */