pgloader - pgloader: Factorize readers file opening code

Log Message:
-----------
Factorize readers file opening code

Modified Files:
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pgloader/examples:
parallel.conf (r1.4 -> r1.5)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgloader/pgloader/examples/parallel.conf.diff?r1=1.4&r2=1.5)
pgloader/pgloader:
csvreader.py (r1.7 -> r1.8)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgloader/pgloader/pgloader/csvreader.py.diff?r1=1.7&r2=1.8)
reader.py (r1.12 -> r1.13)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgloader/pgloader/pgloader/reader.py.diff?r1=1.12&r2=1.13)
textreader.py (r1.14 -> r1.15)
(http://cvs.pgfoundry.org/cgi-bin/cvsweb.cgi/pgloader/pgloader/pgloader/textreader.py.diff?r1=1.14&r2=1.15)