Change open file mode from `rwb` to `r+b`

This manifested as a bug on FreeBSD.

The goal is to get a readable, writable file in "binary" mode (not
it's likely Windows is going to work).  But, spelling that mode "rwb"
seems to be platform specific one.

This way of specifying the mode is not documented by Python, which
prefers "r+" to spell out this intention:
http://docs.python.org/2/tutorial/inputoutput.html#reading-and-writing-files

Conflicts:
	wal_e/worker/upload.py
	wal_e/worker/worker_util.py
Add Petar Radosevic as a contributor
Avoid following symlinks when fsyncing

This can cause a crash with dangling symlinks, which are otherwise
allowed and have a few use cases.  Compare to
9d389e9dc5ef46049a217e731683da56a235bc43 in v0.7:

	The reasons to allow such dead-end symlinks in tarfiles is
	obscure.  Part of this is backwards compatibility with old
	archives that allowed them, presuming they'd later be
	overwritten by the user, interpreted within a chroot, or
	reference a file elsewhere within the same data directory that
	is yet to be extracted by another volume being downloaded.
v0.6.8