Introduced DcmOutputBufferStream::filled() method.

This method allows to query the bytes in buffer without flushing it.
Fixed a problem in storescp.

Storescp aborts if it cannot create files in its working directory.
This behavior is intended, but it should be omitted if the "--ignore"
flag was set, which is realized by this commit.
Modified some of OFoptional's comparison operators.

All comparison operators with an OFoptional object as left hand side
argument are now implemented as member methods instead of friend functions.
This is meant to reduce incorrect overload lookup in some Visual Studio
compilers.
Introduced OFtuple implementing generic tuples.

OFtuple is a fixed-size collection of heterogeneous values. It can be
regarded as a generalization of OFPair.
OFtuple is similar to C++11's std::tuple and can be replaced by
std::tuple via enabling 'DCMTK_USE_CXX11_STL'.
Introduced move emulation for pre C++11 compilers.

C++11's move semantics allow more efficient parameter and especially
return value passing then before. The implemented emulation allows to use
the primary functionality of move semantics in pre C++11 compilers in a way
that automatically translates to the appropriate C++11 syntax when C++11
support is enabled via 'DCMTK_USE_CXX11_STL'.
The only class utilizing move semantics so far is OFunique_ptr, where move
semantics are essential to allow using OFunique_ptr objects as parameters
or return values.
Small fixes for a previous commit about OFtuple.

Removed unnecessary additions to the Doxygen configuration file for
manpages.
Added OFtuple's testcase to the autoconf configuration.
Added 'Purpose' statement to OFtuple's header file.
Several fixes and additions for yesterday's commits.

Guarded remaining friend comparison operators of OFoptional via
OFenable_if. This should finally fix the faulty overload resolution
problem in Visual Studio.
Worked around a limitation in MinGW where const objects could not have
external linkage.
Corrected template-recursion related problem in OFtuple that prevented
compiling with Clang.