ENH: use dictionary::readEntry for detection of input errors (#762, #1033)

- instead of   dict.lookup(name) >> val;
  can use      dict.readEntry(name, val);

  for checking of input token sizes.
  This helps catch certain types of input errors:

  {

      key1 ;                // <- Missing value
      key2 1234             // <- Missing ';' terminator
      key3 val;
  }

STYLE: readIfPresent() instead of 'if found ...' in a few more places.

applications/utilities/miscellaneous/foamHelp/helpTypes/helpSolver/helpSolver.C

@@ -85,7 +85,7 @@ void Foam::helpTypes::helpSolver::execute
     }
     else if (args.found("read"))
     {
-        mesh.time().controlDict().lookup("application") >> solver;
+        mesh.time().controlDict().readEntry("application", solver);
         displayDoc(solver, ".*solvers/.*Foam/", true, "C");
     }
     else

applications/utilities/miscellaneous/foamHelp/helpTypes/helpType/helpType.C

@@ -119,7 +119,7 @@ void Foam::helpType::displayDoc
     {
         const dictionary& docDict =
             debug::controlDict().subDict("Documentation");
-        docDict.lookup("docBrowser") >> docBrowser;
+        docDict.readEntry("docBrowser", docBrowser);
     }
 
     doxygenXmlParser parser