isValid -> supportsEditor

Done with Roberto Raggi

Now it shows immediately when there is only a single signature of a
given method/constructor.

(cherry picked from commit 8b9dd766)

Conflicts:

	src/plugins/cpptools/cppcodecompletion.cpp

Deals with cases like "QString s(", but for the moment doesn't handle
yet "QString const s(".

Done with Roberto Raggi.

(cherry picked from commit fca3ec1f)

Now it shows immediately when there is only a single signature of a
given method/constructor.

Deals with cases like "QString s(", but for the moment doesn't handle
yet "QString const s(".

Done with Roberto Raggi.

Some people don't like this.

It is now possible to choose between case-sensitive or case-insensitive
completion. Also, you can now disable the automatic insertion of braces.