Fix issue Andersbakken#302. In gcc-4.7 this leads to the following er…

…ror:

src/FileManager.cpp: In member function \u2018void FileManager::onFileRemoved(const Path&)\u2019:
src/FileManager.cpp:123:35: error: call of overloaded \u2018remove(const char*)\u2019 is ambiguous
src/FileManager.cpp:123:35: note: candidates are:
In file included from src/rct/rct/Path.h:9:0,
                 from src/FileManager.h:19,
                 from src/FileManager.cpp:16:
src/rct/rct/Set.h:25:10: note: bool Set<T>::remove(const T&) [with T = String]
src/rct/rct/Set.h:34:9: note: int Set<T>::remove(std::function<bool(const T&)>) [with T = String]

This is probably just a bug in gcc-4.7 but calling the function with a
String rather than a const char * fixes the problem.

src/FileManager.cpp

@@ -120,7 +120,7 @@ void FileManager::onFileRemoved(const Path &path)
     const Path parent = path.parentDir();
     if (map.contains(parent)) {
         Set<String> &dir = map[parent];
-        dir.remove(path.fileName());
+        dir.remove(String(path.fileName()));
         if (dir.isEmpty()) {
             mWatcher.unwatch(parent);
             map.remove(parent);