With the version of 1.5a, what is the release date?
CREATE TABLE "table1_2263152_1" (
  "version" text,
  "release_date" text,
  "distribution_mechanism" text,
  "features" text,
  "security_issues" text
);
SELECT "release_date" FROM "table1_2263152_1" WHERE "version"='1.5a';