ARB prog parser: Fix epic memory leak in lexer / parser interface

Anything that matched IDENTIFIER was strdup'ed and returned to the
parser.  However, almost every case of IDENTIFIER in the parser just
dropped the returned string on the floor.  Every swizzle string, every
option string, every use of a variable, etc. leaked memory.

Create a temporary buffer in the parser state (string_dumpster and
dumpster_size).  Return strings from the lexer to the parser in the
buffer.  Grow the buffer as needed.  When the parser needs to keep a
string (i.e., delcaring a new variable), let it make a copy then.

The only leak that valgrind now detects is /occasionally/ the copy of
the program string in gl_program::String is leaked.  I'm not seeing
how. :(

src/mesa/shader/program_lexer.l

@@ -40,7 +40,7 @@
       if (condition) {					\
 	 return token;					\
       } else {						\
-	 yylval->string = strdup(yytext);		\
+	 yylval->string = return_string(yyextra, yytext);	\
 	 return IDENTIFIER;				\
       }							\
    } while (0)
@@ -63,7 +63,7 @@
 	 yylval->temp_inst.SaturateMode = SATURATE_ ## sat; \
 	 return token;					\
       } else {						\
-	 yylval->string = strdup(yytext);		\
+	 yylval->string = return_string(yyextra, yytext);		\
 	 return IDENTIFIER;				\
       }							\
    } while (0)
@@ -71,6 +71,45 @@
 #define SWIZZLE_INVAL  MAKE_SWIZZLE4(SWIZZLE_NIL, SWIZZLE_NIL, \
 				     SWIZZLE_NIL, SWIZZLE_NIL)
 
+/**
+ * Send a string to the parser using asm_parser_state::string_dumpster
+ *
+ * Sends a string to the parser using asm_parser_state::string_dumpster as a
+ * temporary storage buffer.  Data previously stored in
+ * asm_parser_state::string_dumpster will be lost.  If
+ * asm_parser_state::string_dumpster is not large enough to hold the new
+ * string, the buffer size will be increased.  The buffer size is \b never
+ * decreased.
+ *
+ * \param state   Assembler parser state tracking
+ * \param str     String to be passed to the parser
+ *
+ * \return
+ * A pointer to asm_parser_state::string_dumpster on success or \c NULL on
+ * failure.  Currently the only failure case is \c ENOMEM.
+ */
+static char *
+return_string(struct asm_parser_state *state, const char *str)
+{
+   const size_t len = strlen(str);
+
+   if (len >= state->dumpster_size) {
+      char *const dumpster = _mesa_realloc(state->string_dumpster,
+					   state->dumpster_size,
+					   len + 1);
+      if (dumpster == NULL) {
+	 return NULL;
+      }
+
+      state->string_dumpster = dumpster;
+      state->dumpster_size = len + 1;
+   }
+
+   memcpy(state->string_dumpster, str, len + 1);
+   return state->string_dumpster;
+}
+
+
 static unsigned
 mask_from_char(char c)
 {
@@ -308,7 +347,7 @@ ARRAYSHADOW1D             { return_token_or_IDENTIFIER(require_ARB_fp && require
 ARRAYSHADOW2D             { return_token_or_IDENTIFIER(require_ARB_fp && require_shadow && require_texarray, TEX_ARRAYSHADOW2D); }
 
 [_a-zA-Z$][_a-zA-Z0-9$]*  {
-   yylval->string = strdup(yytext);
+   yylval->string = return_string(yyextra, yytext);
    return IDENTIFIER;
 }