add unit test for transacted select (pool exhaustion)

[davidmoten]

Adds previously failing unit test to PR #47, cc @ykrkn

[codecov-commenter]

Codecov Report

Merging #125 (c26655c) into master (9ec7293) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #125   +/-   ##
=========================================
  Coverage     77.58%   77.58%           
  Complexity      669      669           
=========================================
  Files            73       73           
  Lines          2748     2748           
  Branches        240      240           
=========================================
  Hits           2132     2132           
  Misses          509      509           
  Partials        107      107           

Impacted Files	Coverage Δ
...rg/davidmoten/rx/jdbc/TransactedSelectBuilder.java	77.27% <100.00%> (ø)

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