[FS#120] opkg fails with Out of memory on a device with 32 MB of RAM

[LEDE Bugs]

The following task has a new comment added:

FS#120 - opkg fails with Out of memory on a device with 32 MB of RAM
User who did this - Jo-Philipp Wich (jow-)

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We had to revert Felix' original commit due to some issues in opkgs vfork code but I pushed an alternative approach to my staging tree which lets opkg use the external gzip command. As a side effect the opkg binary size is reduced by ~4K.

I would appreciate some testing feedback on http://git.lede-project.org/d692bfec1306a514936eca5805dff6b8fac0ee0e
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=120#comment442