Key 'b' in the browse window spawns a shell in the current directoy.

We first check the $SHELL environment variable of the user for the preferred
shell interpreter. If it's not set, we fall back to the compile time
configured default shell (usually /bin/bash).

Signed-off-by: Thomas Jarosch <thomas.jarosch@intra2net.com>

As per http://dev.yorhel.nl/ncdu/bug/55

Slightly modified patch from Gianluigi Tiesi.
http://dev.yorhel.nl/ncdu/bug/47

Turns out that being able to open an empty directory actually has its
uses:
- If you delete the last file in a directory, you now won't be directed
  to the parent directory anymore. This allows keeping 'd' pressed
  without worrying that you'll delete stuff outside of the current dir.
  (This is the primary motivation for doing this)
- You can now scan and later refresh an empty directory, as suggested by
  #2 in http://dev.yorhel.nl/ncdu/bug/15

Fixes build on NetBSD.

As per http://dev.yorhel.nl/ncdu/bug/31

This is a slightly modified patch contributed at

  http://dev.yorhel.nl/ncdu/bug/35

This has apparently been broken since version 1.7 (v1.6-7-g5db9c2a to be
precise), yet NOBODY TOLD ME!? :-(

The OSS community has left me in despair!

Most of which made sense.

Both microlibraries come from another source, and are not maintained as
part of ncdu. This separation of src/ and deps/ makes the relation more
clear.

Tiny bug fix: The size of an excluded directory entry itself should not
be counted, either. This is consistent with what you'd expect: A cache
directory with thousands of files can easily take up several megabytes
for the dir entry - but from the perspective of a backup system that
recognizes cache dirs - the dir is empty, and therefore shouldn't take
any extra space at all.

Use a macro instead of the global constant `cachedir_tag_signature`.
Use `memcmp` instead of `strncmp`.
Add `has_cachedir_tag` to exclude.h.

(See http://dev.yorhel.nl/ncdu/bug/30)

A new command line parameter allows to filter out directories containing
the proper `CACHEDIR.TAG` file.
See http://www.brynosaurus.com/cachedir/

Ncurses provides a pkg-config module which could be used here. If not
available we fall back to the old detection heuristic.

Signed-off-by: Justin Lecher <jlec@gentoo.org>

I realized that I used addparentstats() with negative values when
removing stuff, so it had to be done this way (without rewriting
everything). It's a simple solution, anyway.

This mostly avoids the issue of getting negative sizes. It's still
possible to get a negative size after refresh or deletion, I'll get to
that in a bit.

They should now be able to cope with file sizes in the full (positive)
range of a signed integer, i.e. 0 bytes to 8 EiB minus one byte. The
size calculation of directories, however, may still overflow and cause
negative integers to be passed around. That should be fixed.

As recent autoconf wants

Makefile is generated by configure, and thus guaranteed to be newer than
ncdu.1, causing make to regenerate ncdu.1 regardless of whether pod2man
is installed or not. That kinda defeats the purpose of including ncdu.1
in the distribution.

This also adds the possibility to combine short options that expect an
argument, e.g. "-xo <file>" or even "-xo<file>".