pgsql: Add function to import operating system collations

Add function to import operating system collations

Move this logic out of initdb into a user-callable function. This
simplifies the code and makes it possible to update the standard
collations later on if additional operating system collations appear.

Reviewed-by: Andres Freund <andres(at)anarazel(dot)de>
Reviewed-by: Euler Taveira <euler(at)timbira(dot)com(dot)br>

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/aa17c06fb58533d09c79c68a4d34a6f56687ee38

Modified Files
--------------
doc/src/sgml/charset.sgml | 2 +-
doc/src/sgml/func.sgml | 40 ++++++++
src/backend/catalog/pg_collation.c | 31 ++++++-
src/backend/commands/collationcmds.c | 154 ++++++++++++++++++++++++++++++-
src/bin/initdb/initdb.c | 166 +---------------------------------
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_collation_fn.h | 3 +-
src/include/catalog/pg_proc.h | 3 +
8 files changed, 229 insertions(+), 172 deletions(-)