Doc: Moved QML "plugins" example to "qmlextensionplugins"

The example generates a plugins.html which collides with the
plugins.html from qtbase repository.

Task-number: QTBUG-32580
Change-Id: I47ce9e00378738f7696672e6e47dd3337bb4fafc
Reviewed-by: Martin Smith <martin.smith@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Fix invalid condition in comparisson.

Thanks to clang (top-of-trunk) pointing out that the unary not operator
only applies to the left-hand side of the equality expression.

Change-Id: I093b447d55995a4122aeac042a506eb56f8b2442
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Fix binop related crashes in the interpreter

if (foo instanceof blah) would crash because we generated a BinOp instruction
with a null aluop pointer. Instanceof, in and add are binops that now require
a context, and thus require a different instruction (BinOpContext). This was
already handled by the traditional binop() of the isel, but not by the binop
expression that can be in a cjump. Centralize the code by calling a common
binop helper from isel binop as well as cjump.

Change-Id: I793ee3eebe56db4c86d5399a783a84be3093fd35
Reviewed-by: Lars Knoll <lars.knoll@digia.com>