Root namespace for exceptions

Prepend backslash to all PHP built-in classes for those who namespace the library.
Added PHP 5.6 and HHVM to travis.
minor #118 Added PHP 5.6 and HHVM to travis. (h4cc)

This PR was merged into the 1.1 branch.

Discussion
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Added PHP 5.6 and HHVM to travis.

Build and tests still run :)

Commits
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9c2d6d1 Added PHP 5.6 and HHVM to travis.
Merge branch '1.1'

* 1.1:
  Added PHP 5.6 and HHVM to travis.
minor #116 Root namespace for exceptions (vlakarados)

This PR was merged into the 2.0.x-dev branch.

Discussion
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Root namespace for exceptions

Prepend `\` (backslash) to all PHP built-in classes for those who namespace the library.

This is quite necessary as while developing it's possible not stumble upon exceptions and this will kill production with an uncaught exception, which has a great chance because this library is mainly used in the core of the application where `try/catch` is used rarely.

Commits
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fac4177 Root namespace for exceptions
Pimple C extension