pgsql: In pg_upgrade, simplify function copy_file() by using pg_malloc(

In pg_upgrade, simplify function copy_file() by using pg_malloc() and
centralizing error/shutdown code.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/6b711cf37c228749b6a8cef50e16e3c587d18dd4

Modified Files
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contrib/pg_upgrade/file.c | 54 ++++++++++----------------------------------
1 files changed, 13 insertions(+), 41 deletions(-)