tst_qsignalblocker: simplify test

This test can assume that the QObject::signalsBlocked property works as
advertized, so just check signalsBlocked() in repsonse to QSignalBlocker
manipulations.

Change-Id: I99e4ef9c4ed05c3840233d92a587636d2d78f59a
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
QFont: add missing qHash overload

The properties that make up the hash value are chosen to be the same as those
that make up QFontDef's op<() and op==(). Indeed, the implementation for QFont
simply delegates to the one of QFontDef, which has been added for this purpose,
but may prove useful in its own right down the line.

The code would greatly benefit from a qHash(qreal) implementation. Lacking
this, the patch uses multiplication with 10000 and qRound64() to convert
the one floating-point property used in the hash to an integer. This is
probably the right thing to do anyway, to avoid epsilon problems.

[ChangeLog][QtGui][QFont] Added qHash overload for this class.

[ChangeLog][QtCore][QHash] Allowed QFont to be used as a key in QHash/QSet.

Change-Id: I2c1cb5d9da53e26cb2c0f1a7c357731e73eea78e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Add qHash() overloads for floating-point types

This implementation is based on GCC's implementation of std::hash<FP>, but only
to the extent of checking for zero before hashing the bits. The bit hasher is
the Qt one; I didn't even look what GCC uses.

The check against 0.0 is mandated by the requirement to have
  \forall x,y: x == y => qHash(x) == qHash(y)
which would be violated for x = 0.0 and y = -0.0 if we only hashed the bits.

Implemented out-of-line to avoid potential FP-comparison warnings, as well
as to be able to use the file-static hash() functions, which gets inlined
unlike qHashBits(), which cannot be.

[ChangeLog][QtCore][QHash/QSet] Allowed to use float, double and long double
as QHash/QSet keys.

Change-Id: I38cec4afb860f17e9f8be7b67544e58b330f8fff
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>