Import fixes from raptor

* const'ify string literals and char pointers that needn't be changed
  - librdfa (start_element): const'ify umap_key
  - librdfa (rdfa_complete_object_literal_triples): const'ifty
    current_object_literal
* (rdfa_init_base): Fix <base href >
* (end_element): Do not call rdfa_complete_list_triples() with no
  new subject [coverity]
* (rdfa_init_base): Fix uri_start dead code [coverity]
* (end_element): Add parent_context check around block [coverity]
* (rdfa_init_base): Check for uri_start before use [coverity]
* librdfa fixes for -Wunreachable-code [clang]
* (rdfa_complete_object_literal_triples) strchr on NULL [coverity]
* (rdfa_complete_object_literal_triples): Need non NULL
  context->xml_literal to do strchr() on it [coverity]
* (rdfa_complete_current_property_value_triples): Remove duplicate
  variable [coverity]
* (rdfa_complete_object_literal_triples): NULL check for
  context->xml_literal [coverity]

c/rdfa.c

@@ -143,11 +143,10 @@ static size_t rdfa_init_base(
    {
       char* base_start = strstr(*working_buffer, "<base ");
       char* href_start = NULL;
-      if(base_start == NULL) {
+      if(base_start == NULL)
          base_start = strstr(*working_buffer, "<BASE ");
-         if(base_start != NULL)
-           href_start = strstr(base_start, "href=");
-      }
+      if(base_start != NULL)
+        href_start = strstr(base_start, "href=");
 
       if(href_start != NULL)
       {
@@ -314,7 +313,7 @@ static void start_element(void *parser_context, const char* name,
 #else
       void** umap = context->uri_mappings;
 #endif
-      char* umap_key = NULL;
+      const char* umap_key = NULL;
       void* umap_value = NULL;
 
       /* if the namespaces are not defined, then neither is the xml:lang */
@@ -338,9 +337,9 @@ static void start_element(void *parser_context, const char* name,
 #ifdef LIBRDFA_IN_RAPTOR
          ns=ns_list[--ns_size];
 
-         umap_key = (char*)raptor_namespace_get_prefix(ns);
+         umap_key = (const char*)raptor_namespace_get_prefix(ns);
          if(!umap_key)
-           umap_key=(char*)XMLNS_DEFAULT_MAPPING;
+           umap_key=(const char*)XMLNS_DEFAULT_MAPPING;
          umap_value = (char*)raptor_uri_as_string(raptor_namespace_get_uri(ns));
 #else
          rdfa_next_mapping(umap++, &umap_key, &umap_value);

c/triple.c

@@ -540,7 +540,7 @@ void rdfa_complete_object_literal_triples(rdfacontext* context)
     * @property. If present, a URI is obtained according to the
     * section on CURIE and URI Processing, and then the actual literal
     * value is obtained as follows: */
-   char* current_object_literal = NULL;
+   const char* current_object_literal = NULL;
    rdfresource_t type = RDF_TYPE_UNKNOWN;
 
    unsigned int i;
@@ -571,7 +571,7 @@ void rdfa_complete_object_literal_triples(rdfacontext* context)
    }
    else if(strlen(context->plain_literal) == 0)
    {
-      current_object_literal = (char*)"";
+      current_object_literal = (const char*)"";
       type = RDF_TYPE_PLAIN_LITERAL;
    }
    else if((context->xml_literal != NULL) &&