Introduce and use FileName::exists()

This can use the faster route through QFileInfo::exist now.

Change-Id: Idb41b5d5185d7f02eacba498fb01f483d95e8d57
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>
Reviewed-by: Christian Stenger <christian.stenger@digia.com>

src/libs/utils/fileutils.cpp

@@ -144,7 +144,7 @@ bool FileUtils::copyRecursively(const FileName &srcFilePath, const FileName &tgt
 {
     QFileInfo srcFileInfo = srcFilePath.toFileInfo();
     if (srcFileInfo.isDir()) {
-        if (!tgtFilePath.toFileInfo().exists()) {
+        if (!tgtFilePath.exists()) {
             QDir targetDir(tgtFilePath.toString());
             targetDir.cdUp();
             if (!targetDir.mkdir(tgtFilePath.toFileInfo().fileName())) {
@@ -551,6 +551,13 @@ QString FileName::toUserOutput() const
     return QDir::toNativeSeparators(toString());
 }
 
+/// \returns a bool indicating whether a file with this
+/// FileName exists.
+bool FileName::exists() const
+{
+    return QFileInfo::exists(*this);
+}
+
 /// Find the parent directory of a given directory.
 
 /// Returns an empty FileName if the current directory is already