BUG #15499: pg_dump does not read connection URL from environmentvariable

The following bug has been logged on the website:

Bug reference:      15499
Logged by:          Yonatan Romero
Email address:      yromero@onapsis.com
PostgreSQL version: Unsupported/Unknown
Operating system:   Ubuntu 14.04 LTS
Description:

pg_dump's docs says this command can use connection string on --dbname
argument[1].

Also, the libpq environments variables's documentation says PGDATABASE
behaves the same as the dbname connection parameter[2].

I try to pass connection string on PGDATABASE environment variable, but it
does work.

yromero@onapsis:~$ env
PGDATABASE="postgresql://onapsis:secret@localhost/onapsis" pg_dump
pg_dump: [archiver (db)] connection to database
"postgresql://onapsis:secret@localhost/onapsis" failed: FATAL:  role
"yromero" does not exist

References:
[1] https://www.postgresql.org/docs/9.3/app-pgrestore.html
[2] https://www.postgresql.org/docs/9.3/libpq-envars.html