fastx: improve ugly 'fgets' hack to avoid compilation warnings.

This change was already included in the previously released
version 0.0.13.2 (but I forgot to add it here).
Enables compiling with "-D_FORTIFY_SOURCE=2".

Solves github issue #1.
build: detect TR1 or C++11 with automake macros.

Used in fastx-collapser, should ease compilation on newer systems.