I've picked resolving this issue as an easy first contribution to Jenkins. First, I'd like to discuss backwards compatibility. Given these <key,value> mappings: <A,a>, <B,b> and <A.B,a-b>. How should $A.B and ${A.B} be evaluated? I think $A.B should evaluate to a.B, as it currently does, and ${A.B} to a-b instead of the current ${A.B}. With that scheme:

1) References to keys with dots must use brackets.
2) Existing ${A.B}-like references will break if there actually is an A.B key defined, which I think is very unlikely.

Is this an acceptable resolution?

It is
Thx

Code changed in jenkins
User: Larry North
Path:
core/src/main/java/hudson/Util.java
core/src/test/java/hudson/UtilTest.java
http://jenkins-ci.org/commit/jenkins/3376cf01580ecd9cd099b5513874c8bed2490839
Log:
[FIXED JENKINS-16660] Allow variable names with dots in bracketed references.

Given these <variable,value> mappings: <A,a> and <A.B,a-b>, $A.B would
evaluate to $a.B, as it currently does, and ${A.B} to a-b instead of the
current ${A.B}.

Existing ${A.B}-like references will break (not evaluate to ${A.B}) if
there actually is an A.B variable defined, which I think is very
unlikely.

Integrated in jenkins_main_trunk #2758

Result = SUCCESS

Code changed in jenkins
User: Larry North
Path:
core/src/main/java/hudson/Util.java
core/src/test/java/hudson/UtilTest.java
http://jenkins-ci.org/commit/jenkins/f664639b79d2dea2abdf48816b01f8ccc525a73f
Log:
[FIXED JENKINS-16660] Allow variable names with dots in bracketed references.

Given these <variable,value> mappings: <A,a> and <A.B,a-b>, $A.B would
evaluate to $a.B, as it currently does, and ${A.B} to a-b instead of the
current ${A.B}.

Existing ${A.B}-like references will break (not evaluate to ${A.B}) if
there actually is an A.B variable defined, which I think is very
unlikely.

(cherry picked from commit 3376cf01580ecd9cd099b5513874c8bed2490839)