Find dsym archive using new naming convention

We gracefully fallback on the old naming convention.
Don’t abort when failing to run subcommand

Fixes #907.
Don’t treat directories as executables

Related to issue #907.
Remove outdated TODO
Dragging last tab from window w/o file browser will close window

Closes #904.
Remove support for disabling file browser status updating

This preference was introduced as a workaround for poor performance when displaying large folders, this however should no longer be an issue.
Use Objective-C literals
Don’t disable NSQuitAlwaysKeepsWindows

This was disabled in an attempt of avoiding the “do you want to open saved documents from last session?” which appear after a crash.

It doesn’t seem to have any effect though, so just noise in the code.
Re-use download window if already visible

This is useful if a new update arrives after TextMate has downloaded the previous update but before the user relaunched TextMate.

Fixes #909.
Move crash reporter info to utility.h
Setup exception handler around editor_t::perform

The implementation of kPaste seems to generate an exception for some users, but I don’t know exactly why, so this should provide some better diagnostics info.
Improve renaming files with hidden extension

We now clear the “hidden extension” flag if the user manually adds it.

We also ensure the hidden extension is not ignored by comparing base name with display name. The flag is ignored under certain circumstances.

Comparing base name with display name alone may give a false positive for localized file names.
Make fs::tree_t member data private
Don’t keep mutex locked longer than required
Checkin release notes
Make helper data type local
Update README
Add an etched effect to the status/action bar dividers
Use divider image from status bars for file browser header
Clean up formatting of selection string