handle long input lines when reading from file

handle long input lines when reading from file

This addresses GitHub isse #377.

Before, input lines longer than the static buffer used to read
data would be handled as if each buffer part were one line.
This could result in splitting input target names into multiple
different target names.

Since the static buffer was significantly smaller then the maximum
length of DNS names (just short of 255 one octet characters),
valid long DNS names could not be read as targets via file.

This commit fixes the splitting of long lines, and also increases
the maximum length of target names to 255 one octet characters.

The additional line parsing code is kept similar to the existing
code and attempts to keep all intended and/or useful features to
minimize the risk of regressions.