This changes 'doom sync' to be smarter about responding to changed
package recipes/pins, changes in Emacs version, or instances where the user
has copied a config to a new system.
In all these cases, the user would formerly have to know about a
specific combination of 'doom sync -u' and 'doom build' to ensure Doom
is in a good state. With this change, 'doom sync' handles all these
cases.
Also, 'doom build' is now deprecated (and 'doom sync' now has a
--rebuild option to mimic its old behavior).
Also also, sometimes, a package may silently fail when cloned (which
used to result in an empty repo). Now, if this is detected, cloning will
be re-attempted up to 3 times before aborting with much more visible
error.
Note: these are stopgap solutions, until v3 is finished.
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