Tell Guile (and others) to look in install/lib/gnucash for libraries.
Without this Guile can't find libgncmod-engine and GnuCash won't start.
I don't know how this worked before, perhaps because the correct path
was in src/bin/overrides/gnucash-env.in
Bug 741228 - "Red line" threshold applies to Template scheduled transactions

Check for a GNC_SX_ID kvp on the split to exclude SX transactions from being blocked.
Extract function to clarify intent.
Revisit "Bug 741810 - Compilation fails because of creating .gnucash"

Use the temp dir as base dir for .gnucash
in all cases where the home dir fails. This
is more than just if the home directory doesn't exist.

Also don't attempt to create the home directory.