ENH: allow '^' as anchor for dictionary scoping (issue #429)

- The existing ':' anchor works for rvalue substitutions
  (Eg, ${:subdict.name}), but fails for lvalues, since it is
  a punctuation token and parse stops there.

applications/test/dictionary/testSubkeyword

@@ -34,15 +34,16 @@ update
         key2 $key1;
         key3 val3;
         key2b ${..key2};
-        key3b ${:key1};
+        key3b $^key1;
     }
 }
 
 
 $update
 
-key3 ${:subdict.key1};
-key3 ${:update.subdict.key3};
+// Can a leading '^' or  ':' as anchor for scoping
+key3 $^subdict.key1;
+key3 ${^update.subdict.key3};
 key4 ${:update.subdict...subdict.key1};
 
 // This is currently not working

src/OpenFOAM/db/dictionary/dictionary.C

@@ -575,7 +575,7 @@ const Foam::entry* Foam::dictionary::lookupScopedEntryPtr
     bool patternMatch
 ) const
 {
-    if (keyword[0] == ':')
+    if (keyword[0] == ':' || keyword[0] == '^')
     {
         // Go up to top level
         const dictionary* dictPtr = this;

src/OpenFOAM/db/dictionary/dictionary.H

@@ -43,7 +43,7 @@ Note
     Within dictionaries, entries can be referenced by using the '$' syntax
     familiar from shell programming. A '.' separator is used when referencing
     sub-dictionary entries. Leading '.' prefixes can be used to specify
-    an entry from a parent directory. A leading ':' prefix specifies
+    an entry from a parent directory. A leading ':' or '^' prefix specifies
     starting from the top-level entry. For example,
 
     \verbatim
@@ -62,7 +62,7 @@ Note
         }
     }
 
-    key4        $:subdict1.subdict2.key3;
+    key4        $^subdict1.subdict2.key3;  // lookup with absolute scoping
     \endverbatim
 
     It is also possible to use the '${}' syntax for clarity.