Fixes #2033.

It most likely was a typo for `da`, and all actually updated
translations are properly listed.

Fix document_account_for_unsaved() so it does not alter the `changed`
flag on documents, in order for plugins to have a reliable value there
at all times.

Patch by @chrontec with small additional tidying up.

Closes #1857.

Autotools: Detect GTK version to use automatically.  GTK2 is still the
default if both GTK2 and GTK3 are present.

* Update zh_CN.po

* Update version number for zh_CN translation

* updated it.po

* Update some copyright times on it.po

This is the default since forever, so don't change it on the users,
no matter what is the new default in Scintilla 3.10.0.

Fixes #2010.

After 3b1c6f36 (PR#2005) a string
slightly changed, so update the translation to match.

* Update of Traditional Chinese translation

* Correct version number on zh_TW.po

Improve goto-symbols popup

- Notably the utils_strv_{find_common_prefix,find_lcs,shorten_file_list}
  now take -1 for num to mean to compute the array length.

- utils_strv_find_common_prefix implementation simplified.

- if num == 0 is passed to the above functions the passed strv is not
  dereferenced (so could be NULL).

- Fix lots of compiler warnings
- Fix a bug where a long base name would prevent ellipsizing the longest
  common substring
- rewrite utils_strv_shorten_file_list to be more clear (hopefully)
- use g_strlcpy
- optimize case where the longest common substring need not be searched for

The array annotation has many possible parameters, this avoids having a Doxygen
command for each one.

Luckily you can define Doxygen commands multiple times with different a number
of parameters each.

Since I based the algorithm of the above function on code in one of my python
plugins, I would like to remove the implementation in my plugin and call
Geany's function.

We can now use @array and @arraylen{param} annotations for arrays that
will make it to the generated gtkdoc header.

g-ir-scanner cannot properly parse 'gchar **' parameters without this.

From #1069:
> At the moment if symbols of the same name are defined in identically named
> files, it's hard to distinguish which file is which because there's no path
> in the popup.

> The popup should show part of the path until a directory where the paths
> differ so it's possible to distinguish the different files. At the same time
> there should probably be some top limit for the length of the paths as they
> can make the popup too wide.

This addresses the above by showing more of the file's paths but still try
to make it as short as possible. The file list is processed by the new
utils_strv_shorten_file_list(), as a result the popup will list files with
the common prefix stripped and the longest common sub-path ellipsized.

As a result, the file list shows enough of the path to make them unique but
still is still very short and doesn't make the dialog too wide.

Fixes #1069.