In some cases snippets have a description. Due to the sorting this
already places them after keywords. So this is just to be consistent
for all cases.

Task-number: QTCREATORBUG-2307
Reviewed-by: Thorbjorn Lindeijer

Done with: Thorbjørn Lindeijer

Don't complete the current item when pressing special characters (e.g. `;') if the completion is automatically triggered.

Done-with: Erik Verbruggen

Don't automatically trigger the completion when editing a word or when
in a comment or string.

Allowing any length more than 2 is too slow at the moment. We'd first
need to find a way to avoid recalculating the complete list of items
for every character while the key isn't matching anything.

Now it's possible to choose between having completion popup manually,
when triggered or always.

Similar behaviour as for the QML editor. However, for now without
removing the completion box when you have typed the whole word, since it
could still be useful for automatically inserting other characters.

Task-number: QTCREATORBUG-67

Done-with: Erik Verbruggen

Now you can type characters like ., ( and : to complete the selected
item, depending on the type of the completion item.

Task-number: QTCREATORBUG-271
Reviewed-by: Roberto Raggi

This was a regression introduced in 8e4fb678
triggersCompletion should return `true' when the token at the left of the T_LPAREN
is an identifier, a SIGNAL, a SLOT or T_GREATER (for template functions).

columnNumber() relies on text wrapping, and we're only interested in the
position of the cursor in the block.

Also removed TokenUnderCursor as it's functionality is in the token cache.

Reviewed-by: ckamm

This reverts commit c2393df0.

This should speed things up a bit, because before, the line was tokenized at
least 3 times.