QmlJS: Support .import directives in js files.

* Allow .import...
* Fix parsing of JS files when using Lexer::scanDirectives()
* Clean up ImportInfo construction.
* Rename ImportInfo::id to ImportInfo::as.

Change-Id: I888da248f06dc6184db99aa74c3b50d7f2f5e491
Reviewed-on: http://codereview.qt-project.org/5625
Reviewed-by: Roberto Raggi <roberto.raggi@nokia.com>

src/libs/qmljs/parser/qmljsengine_p.cpp

@@ -113,7 +113,7 @@ double integerFromString(const QString &str, int radix)
 
 
 Engine::Engine()
-    : _lexer(0)
+    : _lexer(0), _directives(0)
 { }
 
 Engine::~Engine()
@@ -134,6 +134,12 @@ Lexer *Engine::lexer() const
 void Engine::setLexer(Lexer *lexer)
 { _lexer = lexer; }
 
+void Engine::setDirectives(Directives *directives)
+{ _directives = directives; }
+
+Directives *Engine::directives() const
+{ return _directives; }
+
 MemoryPool *Engine::pool()
 { return &_pool; }