timer.h: access to the accumulated time is now const
Added a new class custom_stats for gathering statistical data.
Using the class you can conveniently use counters and timers
and activate/deactivate all of them at compile-time with a single
typedef line.
Added three new macros to verbose.h
    - STXXL_VARDUMP(x) prints the name of x together with its value.
    - STXXL_MEMDUMP(x) prints the name of x together with its value as an amount of memory in IEC units.
    - STXXL_CHECK_EQUAL(a,b) is an assertion macro for unit tests, similar to
        STXXL_CHECK(a==b). The difference is that STXXL_CHECK_EQUAL(a,b) also prints
        the values of a and b. Attention: a and b must be printable with std::cout!
* Added a new bulk-parallel priority queue class for external memory: parallel_priority_queue.h
    The algorithm is described in detail in http://algo2.iti.kit.edu/2386.php

* Added a new benchmark benchmark_pqs.cpp for comparing different priority queue implementations on the same input data.
Replaced the custom_stats class by two classes custom_stats_counter and custom_stats_timer.
This obviates the use of a hash map. Unfortunately there is no longer a print_all() method.
Fixed compilation with the different configurations tested by Travis.
This includes i.a. the removal of implicit casts and STXXL_PARALLEL switches.
Merge branch 'stxxl/master' into master
Uncrustify (reformatting) source.
Replacing custom_stats_timer with timer and fake_timer, which does exactly that.
Templatize the value_type in custom_stats_counter.
Adding static const bool is_real to timer and fake_timer.
Reworking ppq_index_winner_tree: looks good.
Added test for ppq_external_array.h
Moved internal_array class into the ppq_local namespace.
Moved minima_tree class into parallel_priority_queue.h / ppq_local namespace
* Renamed ppq_external_array.h to external_array.h.

* Reorganized imports in external_array.h
* Moved containers/ppq_index_winner_tree.h to algo/winner_tree.h

* Fixed dummy_custom_stats_counter

* Disabled statistics
Smaller test, adding delete of external_array.
Refactoring benchmark_pqs: using abstract container with template specializations, works with bulk_intermixed_check.
Refactoring complete benchmark_pqs.cpp: using abstract container with template specializations instead of macros.