gnu: module-init-tools: Fix $LINUX_MODULE_DIRECTORY handling in 'depmod'.

* gnu/packages/patches/module-init-tools-moduledir.patch: Adjust the
  'depmod' part to handle $LINUX_MODULE_DIRECTORY without a trailing
  slash.

gnu: module-init-tools: Handle $LINUX_MODULE_DIRECTORY without trailing slash.

Fixes <http://bugs.gnu.org/18068>.

* gnu/packages/patches/module-init-tools-moduledir.patch: Adjust to deal
  with the lack of a trailing slash.

Merge branch 'master' into core-updates

system: Tell module-init-tools where to look for modules.

* gnu/packages/linux.scm (module-init-tools)[source](patches): New
  field.
* gnu/packages/patches/module-init-tools-moduledir.patch: New file.
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/system.scm (etc-directory): Add #:kernel parameter.  Set
  'LINUX_MODULE_DIRECTORY' in bashrc.
  (operating-system-etc-directory): Pass #:kernel to 'etc-directory'.