fix handling of --post_category parameter; closes #986
use putenv() instead of relying on Bash inline variables

fixes #1086
Merge pull request #1086 from wp-cli/fix-1086

Cygwin shell doesn't support inline environment variables
wp cache: remove redundant exit calls and use WP_CLI::line()
abort loading if APC object cache is detected

see #283
avoid using wp_using_ext_object_cache() function, which was only introduced in WP 3.7
make search-replace work with tables that have a composite primary key
Merge pull request #1087 from wp-cli/fix-1049

make search-replace work with tables that have a composite primary key