Use the Composer autoloader when running tests

Right now we expect PHPUnit to be installed globally or with pear.
Now we try to figure out where the Composer's autoload.php is
and load it if we found it. This will fix the loading of PHPUnit
for Agavi apps which load Agavi via Composer as well.

closes #1473
fix ticket number in changelog
Fix PHP 5.3 compatibility, refs #1473
No more warnings in "shiny" exception template if headers were already sent
Not raise any errors in "shiny" exception template if $context or $container are not defined
Always open the trace in "shiny" exception template if only a single stack entry is given
add CHANGELOG for #1478
Merge ac2ca4f...865bd9a (from pr-1478)

closes #1478

* exception-template:
  865bd9a add CHANGELOG for #1478
  cc0fc67 Always open the trace in "shiny" exception template if only a single stack entry is given
  f854f88 Not raise any errors in "shiny" exception template if $context or $container are not defined
  ac2ca4f No more warnings in "shiny" exception template if headers were already sent
Merge a1290d6...94052e5 (from 1.0)

* 1.0:
  94052e5 Merge ac2ca4f...865bd9a (from pr-1478)
  865bd9a add CHANGELOG for #1478
  cc0fc67 Always open the trace in "shiny" exception template if only a single stack entry is given
  f854f88 Not raise any errors in "shiny" exception template if $context or $container are not defined
  ac2ca4f No more warnings in "shiny" exception template if headers were already sent
  9bb0a59 Fix PHP 5.3 compatibility, refs #1473
  bb5a1de fix ticket number in changelog
  a1290d6 Use the Composer autoloader when running tests