BUG/MEDIUM: compression: fix the output type of the compressor name

smp_fetch_res_comp_algo() returns the name of the compression algorithm
in use. The output type is set to SMP_T_STR instead of SMP_T_CSTR, which
causes any transformation to be operated without a cast. Fortunately,
the current converters do not overwrite a zero-sized area, so the result
is an empty string. Fix this to have SMP_T_CSTR instead so that the cast
is always performed using a copy before any transformation is done.
BUG/MEDIUM: map: The map parser includes blank lines.

The parser check the end line comparing to the null character.
In fact, the end of line can be also '\r' or '\n'.

The effect is that empty lines are loaded and indexed in maps.

The bug was introduced by commit d5f624dd ("MEDIUM: sample:
add the "map" converter") in 1.5-dev20. No backport is needed.