Export realiseContext in libnixexpr

Useful for importNative plugins
Drop support for pre-c++11 compilers.

In particular, gcc 4.6's std::exception::~exception has an exception
specification in c++0x mode, which requires us to use that deprecated
feature in nix (and led to breakage after some recent changes that were
valid c++11).

nix already uses several c++11 features and gcc 4.7 has been around for
over 2 years.
Improve printing of ASTs
Revert "Drop support for pre-c++11 compilers."

The breakage this fixed can be worked around without removing support.

This reverts commit 84a13dc576496f1227665259c61f86184f452f51.
Fix build on gcc < 4.7
Temporarily disable darwin builds while hydra's darwin is borked
Merge pull request #380 from shlevy/temp-disable-darwin

Temporarily disable darwin builds while hydra's darwin is borked
doc: fixed nix-instantiate --find-file

The manual said --file-file, which should be --find-file.
Remove comments claiming we use a private PID namespace

This is no longer the case since
524f89f1399724e596f61faba2c6861b1bb7b9c5.
Document some primops
Update release notes
Revert "Temporarily disable darwin builds while hydra's darwin is borked"

This reverts commit 29f7e142fc5d01fd2703c70442dc06fd98ce9595.
Revert "Revert "Temporarily disable darwin builds while hydra's darwin is borked""

This reverts commit f72944b42f7504ed73129395a2636d3a4ecabf4e.
Shut up a clang warning
Fix more warnings
Don't pull in git when doing a nix-shell
Revert "Revert "Revert "Temporarily disable darwin builds while hydra's darwin is borked"""

This reverts commit a51f8d67473953307ef7fd0ea033a81fb022289f.
Improve error message if the daemon worker fails to start
nix-daemon: Get peer credentials on Mac OS X

This makes allowed-users and trusted-users work on Mac OS X.
Typo