pgsql: pg_upgrade: prefix Unix shell script name output with "./"

pg_upgrade:  prefix Unix shell script name output with "./"

This more clearly suggests the current directory.  While this also works
on Windows, it might be confusing.

Report by Christoph Berg

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/dc9c612767f20f28f35f06d709d59ed8477bfe32

Modified Files
--------------
contrib/pg_upgrade/check.c      |    6 ++++--
contrib/pg_upgrade/pg_upgrade.h |    2 ++
2 files changed, 6 insertions(+), 2 deletions(-)