Fixes an issue where client applications such as ssh might attempt to
close all open fds, therefore also closing the fds used by the internal
components of the library such as Mercury.

If we intercept function during shutdown we could try to access the
internal file map that has been already freed.

This woun't affect performance at runtime since we are always checking
only one boolean flags on every interception as before.

On the other hand should sppedup the shutdown of the library, because we
disable the interception of glibc library call before performing the
shutdown routines.

when resolving path we don't want always
to resolve also the last components if it is a link. Cause in some cases
we want exactly the path of that link and not the one it points to.

lstat and readlink are some example of functions that don't want to
resolve the last link.

relativize path now accepts a file descriptor.

If fd is AT_FDCWD relative path need to be considered with respect to
the current working directory. Otherwise the path is relative to the
directory with the given file descriptor

add support for path resolution, this will be used to get canonical path.

More info at `man path_resolution`

During interception library startup the CWD of intercepted process is
stored in the PreloadContext object

Mercury now support shared memory autorouting.

A single margo instance can be initialized and it will handle both
shared memory communication and remote ones.

If the endpoint of the RPC is local mercury will automatically use
shared memory.

Since there is only one margo instance all the duplicated code for
rpc/ipc have been unified and simplified considerably.

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The way in which client contact the server has changed.

 - Server initializes its own margo instance and generate the endpoint
communication string using `HG_Addr_self`.
 - This endpoint description string is written on the pid file
 - When the client library loads it will fetch the server endpoint
description from the pid file and will use that to contact the server.

The library intercepts IO functions from others library constructors
before our constructor have been executed.

All the interceptions triggered before that our constructor have been
executed are now forwarded to the glibc.

By moving the logger initialization outside of the passthrough
initialization we will be able to implements fopen interceptions.

Paths are now made relative to the mountdir at client side.

The new relativize_path fucntion in the PreloadContext is used to check
if a path is relative to the pseudo-mount directory and to make it
relative

The new PreloadContext class is used as singleton to store the general context
information of the interception library.

The plan is to move global accessed variables into this sigleton.

At the moment just the logger object has been moved into it.