Currently only the list of hard coded terminal names found in
_legal_terms_re allow usage of the title setting feature. Maintaining
this list is a burden and means that some terminals will miss out this
feature, although they actually do have support for it.

Thus, try to use the curses module to dynamically query the terminfo
database for "tsl" (to status line) and "fsl" (from status line)
strings. This way all terminals that declare support for the feature
will automatically benefit.

As a fallback, should curses not be available, still rely on the
_legal_terms_re for setting up terminal titles.

Signed-off-by: Matthias Gerstner <[email protected]>

The global variables are inconsistently named and spread over the
module, similarly the title related code is not grouped together.
Harmonize this.

Also the double negative logic involving `_disable_xtermTitle` makes the
code harder to read. Invert the logic.

Signed-off-by: Matthias Gerstner <[email protected]>

sys.stderr is sometimes temporarily replaced by other objects, thus rely
on sys.__stdserr__ consistently. Also provide a default for `fd` in
`init_curses()`.