The convention in Maneage for bracketting in makefiles is (it
seems to me) to use $(round brackets), not ${curly brackets}, at
the 'make' level, and $$nobracketsnorunderscores for variables
intended to pass through to the bash shell; while our convention
in elaphrocentre modifies this to use
$${curly_brackets_and_allow_underscores} for variables to be
passed through to bash scripts. However, sometimes we haven't
followed this convention fully.

According to the GNU make manual [1], ${curly brackets} are
just as valid as $(round brackets) at the 'make' level,
but mixing the two types is discouraged.

This commit hypothesises that there is a bug in the GNU make
ore the GNU bash implemention in macOS/Darwin/xnu that
occurs when a colon ':' is included indirectly (through nesting)
in a ${curly_bracket}, by improving the consistency of using
round brackets in `reproduce/analysis/make/analyse-plot.mk`.

(Some locale variables are also explicitly set to English in
`reproduce/analysis/bash/run-plots`.)

In principle, this commit should not cause any difference
in behaviour of the pipeline. However, it might fix
a bug in macOS/Darwin/xnu.

[1]: https://www.gnu.org/software/make/manual/html_node/Syntax-of-Functions.html#Syntax-of-Functions