pgsql: Print file name and errno string on rmtree failure.

Log Message:
-----------
Print file name and errno string on rmtree failure.

Backpatch to 8.0.X.

Tags:
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REL8_0_STABLE

Modified Files:
--------------
pgsql/src/port:
dirmod.c (r1.34 -> r1.34.4.1)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/port/dirmod.c.diff?r1=1.34&r2=1.34.4.1)