Fix a problem where internal flex buffers were not getting properly

reset when scanning a second file.

This commit was SVN r3158.

src/mca/base/mca_base_parse_paramfile.c

@@ -31,6 +31,7 @@ int mca_base_parse_paramfile(const char *paramfile)
     }
 
     mca_base_parse_done = false;
+    mca_base_param_init_buffer(mca_base_yyin);
     while (!mca_base_parse_done) {
         val = mca_base_yylex();
         switch (val) {

src/mca/base/mca_base_parse_paramfile_lex.h

@@ -20,7 +20,8 @@
 
 #include <stdio.h>
 
-extern int mca_base_yylex(void);
+int mca_base_yylex(void);
+int mca_base_param_init_buffer(FILE *file);
 
 extern FILE *mca_base_yyin;
 extern bool mca_base_parse_done;

src/mca/base/mca_base_parse_paramfile_lex.l

@@ -62,8 +62,27 @@ static int finish_parsing(void)
     return YY_NULL;
 }
 
+
 static int mca_base_yywrap(void)
 {
     mca_base_parse_done = true;
     return 1;
 }
+
+
+/*
+ * Ensure that we have a valid yybuffer to use.  Specifically, if this
+ * scanner is invoked a second time, finish_parsing() (above) will
+ * have been executed, and the current buffer will have been freed.
+ * Flex doesn't recognize this fact because as far as it's concerned,
+ * its internal state was already initialized, so it thinks it should
+ * have a valid buffer.  Hence, here we ensure to give it a valid
+ * buffer.
+ */
+int mca_base_param_init_buffer(FILE *file)
+{
+    YY_BUFFER_STATE buf = yy_create_buffer(file, YY_BUF_SIZE);
+    yy_switch_to_buffer(buf);
+
+    return 0;
+}