pgsql: pg_upgrade: quote directory names in delete_old_cluster script

pg_upgrade:  quote directory names in delete_old_cluster script

This allows the delete script to properly function when special
characters appear in directory paths, e.g. spaces.

Backpatch through 9.0

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/08aaae40e18e89065b191dbcaae54ab87ce63979

Modified Files
--------------
contrib/pg_upgrade/check.c |    6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)