fix return type of expect.

originally reported by @chandrashekhar-vastrad
Merge pull request #9 from kzk/fix-expect

fix return type of expect.
Fix clang++ compiler warning: control may reach end of non-void function

Squashed commit of the following:

commit f708cd5ebe6280704e413657057aaf142c9772c5
Author: Mikael Lund <Mlund@mac.com>
Date:   Fri Jan 25 09:23:01 2013 +0100

    Update picojson.h

    fix previous commit to right line

commit 51d68f5bfad3afa84ad9a8e6db577bd22caf9ea4
Author: Mikael Lund <Mlund@mac.com>
Date:   Fri Jan 25 09:21:20 2013 +0100

    Update picojson.h

    Fix clang++ compiler warning: control may reach end of non-void function.
include float.h for testing
name the union
implement swap(), add tests by Egtra <yusuke.ichinohe@gmail.com>
Merge branch 'kazuho/swap'
Merge branch 'kazuho/master'