Put back autoloading of classes in ns + workaround for ROOT-6094

Merge of two commits:

Revert "Revert "Revert "Revert "Enable autoloading of classes in namespaces""""

This reverts commit 16d1b2c0db79ba64eed134b6f65b1a07734fb72c.

Workaround for ROOT-6094

Some facts:
1) Autoloading of classes in namespaces requires empty namespaces
in the rootmaps
2) If a namespace exists *empty* and a library is loaded whic has
overloaded functions in that namespace,  from within PyROOT, those
overloaded functions cannot be used.
3) We workaround this adding an empty anonymous namespace within
the namespaces to allow the usage of such functions.
Blanks.
Blanks.
We don't build libclang.a anymore, depend on libclangSema.a
80cols.
Implement reloading on .L

We keep the FileEntry -> Transaction mapping so that next time there is .L
we can figure out that it was already loaded and unload it and reload it again.
Use proper size_t instead of ssize_t which is not defined in MSVC
Continue iteration even if the first context is empty (part of ROOT-6094).
Roll back workaround of ROOT-6094

proper fix is in.
Remove the stamp and use the ALLHEADERS variable
If the value is not set (due to errors in the runtime evaluation), return default.
Give access to function overloads (ROOT-6094).

Re-implements THashList::GetListForObject() - as if this "THashList" has a gasillion objects and thus each bucket only contains one name.
The lists of overloads are cached to prevent heap allocations unless an update is needed.
PyROOT can now query the overloads if no matching overload is known to it; GetListForObject() will retrieve all currently known overloads of all matching decl contexts and generate TFunction / TMethod objects for them.
Fix doxygen.
Manual focus management.
Trailing blanks
Implement cling::Transaction unique id.
Create output results directory if does not exists.
This fixes ROOT-5481
Apply fixes in copy ctor and assignment op. for Coverity
Add missing include file (unistd.h) defining ssize_t
Fix the PrintXML according to HistFactory.dtd  (InputFileLow/High -> HistoFileLow/High)
This fixes ROOT-5480