(cherry picked from commit ad5b7fce74a3b7b0ed726620c81ea552c643cdad)

(cherry picked from commit 2faefc3b2432409f3ccca0b6ab53a228d5b9b00d)

(cherry picked from commit 32b77d0064d3e5f52e9204ddeffc29bb21a67753)

(cherry picked from commit ce7036d249b6f05633c343ab95d88552aab85402)

(cherry picked from commit 9801f46ece0ca2525f02d71464efc42296dddcb5)

(cherry picked from commit e4e8ebd9e0037812436a1588809deb23e0f3751a)

* Use AS_HELP_STRING instead of deprecated AC_HELP_STRING
* Use AC_OUTPUT without arguments
* Enclose AC_INIT argument in brackets
* Add automake option std-options

(cherry picked from commit 53a33e1db2c9a58b867f7db26c5f476c3ee4b00b)

(cherry picked from commit fd75bd0c22a0ab6935ac5332999ebe77c6d8a1c8)

Fixes #141

Reduces memory by a tiny bit. Arguably we never needed tombstones
because entries are never removed, so there shouldn't be any performance
hit there. We don't even need a 'used' flag either, considering that can
be represented by a NULL value, but I'm not really up for
implementing/modifying my own hash table.

ref: https://attractivechaos.wordpress.com/2019/12/28/deletion-from-hash-tables-without-tombstones/

They were defined (rather than just declared) in .h files, when they
really should be defined in at most a single .c file.

Fixes #140.

I assumed that ./configure would fail if it can't find a suitable
compiler for the given --host, but it just falls back to the host gcc.

Fixes #138

Fixes #135

Broken in 77aca35f
Fixes #134

This is a best-effort approach to save ncdu state when memory is low.
There's likely allocation in libraries that isn't being checked
(ncurses, printf).

Fixes #132 (it actually doesn't, that needs a 64bit static binary too,
but I'll get to that)

Fixes #128.

This allocation is currently leaked, but as long as we don't allocate
new ones for each refresh, that shouldn't be much of an issue.

(cherry picked from commit 9dc2d32a8fb557112f8f96cd14d50b934543ce39)

stat_to_dir() assumes that buf_dir is clean; calling it twice breaks
that asumption.

Symlink loops are handled by the stat(2) syscall. Symlinks pointing to a
directory are ignored (to avoid loops in the recursive scan).

This adds an 'm' command to show the latest modified time of all files
in a directory. The 'M' command allows for ascending and descending
mtime sorting. These are only enabled with the -e flag and overload
the dir_ext mtime field.

I had taken care to not sort empty directories during dirlist_open(),
but forgot that manual user actions can still cause dirlist_set_sort()
to be called, which does not handle empty directories.

Reported by Alex Wilson.

https://dev.yorhel.nl/ncdu/bug/125

Based on https://dev.yorhel.nl/ncdu/bug/124

Implements https://dev.yorhel.nl/ncdu/bug/43

Ought to fix https://dev.yorhel.nl/ncdu/bug/115

https://dev.yorhel.nl/ncdu/bug/112

https://dev.yorhel.nl/ncdu/bug/111