support inlining of non-outermost call expressions

support inlining of non-outermost call expressions

Commit 253cd82 (support inlining of outermost call expressions,
Tue Aug 11 14:10:38 2015 +0200) introduced support for inlining
outermost call expression.  Allow inlining outer call expressions
as well.

In particular, allow inlined functions to have a return statement
at the end and replace this return statement by a write to
a freshly created variable.  The calls in the original statement
and in arguments to outer inlined functions are replaced by reads
from these variables.

Signed-off-by: Sven Verdoolaege <skimo@kotnet.org>