Make find_and_modify die on error

run_command returns a string for errors.  This commit detects it
and rethrows.  Otherwise find_and_modify dies trying to treat
the string as a hash reference and the original error is lost.

A better fix (with broader implications) is to have run_command throw
errors instead of returning strings for errors.
Cache constructor arguments for use with multiple hosts

With multiple hosts, MongoClient creates a subordinate MongoClient
object for each host.  The existing code only used a subset of
arguments, which can cause connection problems (like omitteing 'ssl').

This commit caches the full set of constructor arguments and uses them
all (suitably overridden) when creating subordinate server connections.
fix failing t/gridfs.t
Merge pull request #80 from dagolden/topic/fix-find-and-modify-error-handling

Make find_and_modify die on error
Merge pull request #83 from dagolden/topic/fix-gridfs-test

fix failing t/gridfs.t
Merge pull request #82 from dagolden/topic/fix-get-master-with-auth-and-ssl

Cache constructor arguments for use with multiple hosts
Integrated libbson for perl_mongo_*_to_sv

Replaced existing buffer iteration with the use of libbson's bson_reader
and bson_iter interface.

Maintained existing perl_mongo_bson_to_sv behavior in
perl_mongo_buffer_to_sv.
Migrated to libbson's bson_append_*

Using libbson's bson_append in favor of direct internal buffer
management
Merge pull request #84 from hanumantmk/libbson_integration

Libbson integration
tweaking build system for libbson integration
PERL-285 add wire protocol check
PERL-285 tests for wire protocol check
PERL-267 memory leak fixes. plus, making sure libson is linked when building
Merge pull request #85 from rojasc/master

PERL-267 memory leak fixes. plus, making sure libson is linked when buil...
remove libbson from @cc_lib_links
Merge branch 'master' of github.com:mongodb/mongo-perl-driver
PERL-285 skip wire proto check in tests on older drivers
PERL-258 remove resultNs logic for $out results
PERL-258 update tests for $out results to manually grab collection
PERL-278 added explain support for aggregate