Ensure tmux-256color exists on macOS

As outlined in [this
gist](https://gist.github.com/bbqtd/a4ac060d6f6b9ea6fe3aabe735aa9d95)
the version of `ncurses` shipped with macOS is too old to be aware of
the `tmux-256color` terminal info database which is the default in
`tmux`. This patch downloads the latest `ncurses` terminal info database
and uses that to install the `tmux-256color` entry for the current user
in `~/.terminfo`. This ensures that bold, italic, etc, are working
correctly and `git` does not throw warnings as noted
[here](1e2c00aa32)

roles/tmux/tasks/Darwin.yaml

@@ -7,3 +7,38 @@
       - reattach-to-user-namespace
       - urlview
     state: latest
+
+- name: check terminal info description exists
+  command: /usr/bin/infocmp -x tmux-256color
+  changed_when: false
+  failed_when: false
+  register: terminfo_exists
+
+- name: download latest terminal info descriptions
+  when: terminfo_exists.rc == 1
+  get_url:
+    url: https://invisible-island.net/datafiles/current/terminfo.src.gz
+    dest: ~/terminfo.src.gz
+
+- name: extract latest terminfo info descriptions
+  when: terminfo_exists.rc == 1
+  command: /usr/bin/gunzip ~/terminfo.src.gz
+
+- name: compile terminal info
+  when: terminfo_exists.rc == 1
+  command: /usr/bin/tic -xe tmux-256color ~/terminfo.src
+
+- name: cleanup downloaded terminal info descriptions
+  when: terminfo_exists.rc == 1
+  file:
+    path: '{{item}}'
+    state: absent
+  with_items:
+    - ~/temrinfo.src.gz
+    - ~/terminfo.src
+
+- name: check terminal info description exists
+  when: terminfo_exists.rc == 1
+  command: /usr/bin/infocmp -x tmux-256color
+  changed_when: false
+  register: terminfo_exists